625 Technical Terms · Polygraph Science A–Z
Polygraph Testing Glossary
The most comprehensive polygraph terminology reference available online. Over 620 technical terms covering polygraph examination techniques, scoring methodologies, psychophysiological measurements, instrumentation, legal standards, and professional practice — an essential reference for examiners trained to APA standards, polygraph students, legal professionals, and anyone preparing for a polygraph examination.
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parameter
In PDD, parameter denotes a single physiological data channel — Pneumograph, cardiograph, electrodermal, or Plethysmograph. The term distinguishes individual recording channels from the multi-chann...
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About this glossary
This glossary is the most comprehensive polygraph and lie detector terminology reference available online — covering everything from foundational concepts like electrodermal activity (EDA), comparison question tests (CQT), and autonomic nervous system responses, to advanced scoring methods including OSS-3, PolyScore, and the Empirical Scoring System (ESS).
Whether you're preparing for an APA-accredited polygraph training program, studying for a professional examiner certification, conducting polygraph research, or simply want to understand how a polygraph works before booking a lie detector test, this resource defines every key term you'll encounter in the field of psychophysiological detection of deception (PDD).
Includes terminology from the American Polygraph Association (APA), the National Center for Credibility Assessment (NCCA), the National Academy of Sciences (NAS) review, and over 100 years of polygraph science — from Marston's blood pressure deception test (1921) to modern computerised polygraph instruments and validated accuracy research.
Complete Polygraph Glossary
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3
3-position scale Scoring
The 3-position scale is an abbreviated form of the 7-position scale used for polygraph test data analysis. Response values range from -1 to +1 rather than the -3 to +3 range of the 7-position system.
7
7-position scale Scoring
The 7-position scale is the most widely used system for assigning numerical values to physiological responses in PDD test data analysis. Values are whole numbers between -3 and +3.
A
a posteriori Practice
A posteriori (Latin: \"from what comes later\") refers to decisions, analyses, or conclusions made after an experiment or test has been conducted. In polygraph research, a posteriori decisions include post hoc statistical analyses of data not anticipated before the study began.
a priori Practice
A priori (Latin: \"from what precedes\") refers to decisions, criteria, or parameters established before conducting an experiment. In polygraph science, a priori decisions include the scoring algorithm to use, sample sizes, and significance thresholds for determining test outcomes.
Accuracy Results
The ability of a polygraph technique to produce correct results. Accuracy varies by technique and the number of relevant questions asked. APA meta-analyses show that validated specific-issue tests using approved scoring methods can exceed 90% accuracy (excluding inconclusive results). Accuracy is measured across sensitivity (detecting deception) and specificity (confirming truthfulness). Learn more about polygraph accuracy rates and research.
Accusatory Approach Techniques
An interviewing style in which the examiner directly confronts the examinee with the assertion that deception has been detected. Associated with the Reid interrogation method. Modern APA standards caution against overly accusatory post-test approaches and emphasise non-coercive interviewing techniques to obtain reliable admissions.
acetylcholine Physiology
Acetylcholine (ACh) is a neurotransmitter found in motor nerves, both divisions of the Autonomic Nervous System, and postganglionic sympathetic nerves to the eccrine sweat glands.
Acquaintance Test Practice
A short, unscored polygraph test administered before the actual examination. Used to demonstrate the polygraph process to the examinee, verify sensor attachment, assess physiological responsiveness, and build rapport. Also called a demonstration or practice test.
A device placed on the seat or under the feet of the examinee that detects body movements during the polygraph examination. Used to identify physical countermeasure attempts and distinguish movement-related artifacts from genuine psychophysiological responses.
Adaptive Questioning Scoring
A testing approach in which subsequent questions or test presentations are adjusted based on the examinee's physiological responses to earlier questions. Used in some Concealed Information Test protocols to improve efficiency. Distinguished from standardised fixed-sequence question formats used in most CQT examinations.
Admission Practice
A voluntary statement made by the examinee during the pre-test or post-test interview acknowledging relevant behaviour or information. Admissions may arise when the examinee is confronted with test results or during question review. All admissions must be documented in the examination report and are separate from the polygraph data itself.
Adrenal Response Physiology
The release of adrenaline (epinephrine) and cortisol from the adrenal glands as part of the sympathetic nervous system's stress reaction. Triggers measurable increases in heart rate, blood pressure, and sweat gland activity — the core physiological changes detected by the polygraph during deception-related arousal.
Adrenalin Physiology
Adrenalin is the trademark name for epinephrine, a hormonal stimulator of the sympathetic nervous system discovered by J. Takamine in 1901. \"Adrenaline\" is the common British term while \"epinephrine\" is preferred in American scientific literature.
adrenergic Physiology
Adrenergic refers to neurons that release the neurotransmitter norepinephrine, as well as substances that mimic norepinephrine's physiological effects. Most postganglionic sympathetic nerves are adrenergic, meaning they use norepinephrine to transmit signals to target organs.
afferent nerves Physiology
Afferent nerves (also called sensory nerves) are nerve fibres that carry impulses from the body's periphery toward the central nervous system. They transmit sensory information — touch, pain, temperature, and proprioception — from receptors throughout the body to the brain and spinal cord for pro...
An APA-validated polygraph testing technique originally developed for the U.S. Air Force. Used primarily in multi-issue screening examinations. Features a structured question sequence designed for counterintelligence and security screening applications.
alarm reaction Physiology
The alarm reaction is the first stage of Hans Selye's General Adaptation Syndrome — the body's three-stage response to stressors. It is triggered by the impact of a stressor and characterised by heightened sympathetic nervous system activity.
Algorithm Scoring
A defined set of mathematical decision rules applied to polygraph physiological data to produce a numerical score and probability estimate of deception or truthfulness. Modern polygraph algorithms include OSS-3, PolyScore, ESS, and CPS Elite. Algorithms analyse respiratory, electrodermal, and cardiovascular data to reduce subjective interpretation.
all-or-none law Physiology
The all-or-none law states that a neuron will respond to its greatest ability or not at all. Stimuli that do not meet or exceed the neuron's threshold will not cause a response; once the threshold is met, the neuron fires at full capacity regardless of stimulus strength.
allostasis Physiology
Allostasis is a concept describing how the brain and body maintain stability through change. Unlike the older concept of homeostasis (maintaining fixed set points), allostasis recognises that regulatory systems have no fixed set point and continuously adjust to meet environmental demands.
alpha Scoring
Alpha (α) is the probability of incorrectly rejecting a true null hypothesis in statistical testing — essentially, the risk of concluding there is an effect when there is none. It represents the probability of making a Type I or false positive error.
American Association of Police Polygraphists Organisations
The American Association of Police Polygraphists (AAPP) is a professional organisation dedicated to serving the needs of criminal justice and military PDD examiners. Founded in 1977, the AAPP has approximately 1,500 members and is headquartered in Waynesville, Ohio.
American Polygraph Association Organisations
The American Polygraph Association (APA) is the largest professional organisation for PDD professionals worldwide, with approximately 2,800 members from law enforcement, government, and the private sector. Incorporated in 1966 in Washington, D.C., the APA resulted from the merger of several earli...
The Americans with Disabilities Act (ADA) is U.S. federal legislation establishing a comprehensive prohibition against discrimination on the basis of disability. The ADA has significant implications for the types of questions that can be asked during pre-employment polygraph screening.
A polygraph testing method developed for U.S. Army use. Note: this technique does not currently meet APA requirements for validation and is not recommended for diagnostic use. Included here for historical reference.
Amplitude Physiology
The magnitude or height of a physiological response as recorded on a polygraph tracing. In electrodermal activity, amplitude refers to the peak conductance change from baseline. In cardiovascular data, it refers to pulse wave height. Amplitude differences between responses to relevant and comparison questions are a primary scoring feature in both manual and automated analysis.
anacrotic limb Physiology
The anacrotic limb is the ascending (upward) portion of an arterial pulse wave as recorded on the polygraph's cardiovascular channel. It represents the phase of the cardiac cycle when the heart's ventricle contracts (systole) and forces blood into the aorta, rapidly increasing arterial pressure.
Analog Polygraph Instruments
A legacy polygraph instrument that recorded physiological data onto continuous paper strips using mechanical pens. Used from the 1920s through the early 2000s before being replaced by digital computerised polygraph systems. Data analysis required manual chart review and hand scoring.
analysis spot Scoring
An analysis spot is the specific location on a polygraph chart where the spot analysis concept is applied. Each analysis spot is generally anchored to a relevant question in the test sequence.
anecdote Practice
An anecdote is a personal narrative relating to an issue or event. In polygraph science, anecdotal evidence refers to non-empirical observations — individual case stories or informal reports that, while potentially interesting, do not constitute scientific proof.
A concept introduced by Cleve Backster describing a phenomenon where a deceptive examinee's concern over the most threatening relevant question results in dampened responses to other relevant questions — even those the examinee is also deceptive about. Explains why examinees sometimes react to only one relevant question when deceptive on multiple issues.
aorta Physiology
The aorta is the main systemic artery from the heart. It receives blood from the left ventricle through the aortic valve and distributes it to all parts of the body through its ascending, arch, and descending segments.
The world's largest professional association of polygraph examiners. Founded in 1966, the APA establishes industry standards for training, practice, ethics, and continuing education. APA accreditation is required by most federal agencies and private employers. Publishes the peer-reviewed journal Polygraph.
APA Code of Ethics Practice
The ethical standards established by the American Polygraph Association governing professional conduct for all APA members. Covers informed consent, examiner competence, conflicts of interest, confidentiality, reporting integrity, continuing education requirements, and prohibitions against discrimination. Violations may result in suspension or expulsion from APA membership.
APA-Accredited School Practice
A polygraph training institution that meets the American Polygraph Association's educational standards, including a minimum of 400 hours of instruction covering physiology, psychology, instrumentation, question formulation, scoring, ethics, and supervised practice examinations. Graduation from an APA-accredited school is required for APA membership and most federal and state examiner positions. See choosing a polygraph examiner for what to look for.
Apnea Physiology
A temporary cessation of breathing observed in polygraph respiratory tracings. Typically occurs near the end of the expiratory segment and is distinguished from "blocking" (which occurs near the inspiratory peak). Apnea may indicate a stress response, a deliberate countermeasure attempt, or a medical condition. Examiners must differentiate between involuntary and deliberate apnea during chart analysis.
Arousal Physiology
A state of physiological and psychological excitement. Lacey (1967) proposed three types relevant to polygraph science: behavioural arousal (observable outward responses), autonomic arousal (measurable psychophysiological changes in the peripheral nervous system), and cortical arousal (EEG desynchronisation). Differential arousal theory is one explanation for how polygraph testing detects deception.
arrhythmia Physiology
An arrhythmia is any variation from the heart's normal rhythm. Regular variations associated with breathing are called sinus arrhythmias. Irregular variations include premature ventricular contractions (PVCs), heart block, flutter, fibrillation, and other ectopic beats. Rapid arrhythmias are term...
Arther Technique Techniques
A probable-lie comparison question technique developed by Richard O. Arther, built upon the Reid school methods. Features a known-truth pseudo-relevant question in the test sequence. The technique relies heavily on behavioural indicators alongside physiological data to assess deception. Historically significant but less commonly used in modern practice.
Artifact Physiology
Any observable change in a polygraph recording not caused by a psychophysiological response to a test question. Common artifacts include coughs, sneezes, body movements, premature ventricular contractions (PVCs), external noise, or equipment malfunction. Artifacts must be identified and excluded from scoring to maintain data integrity.
An international standards organisation that develops and publishes voluntary technical standards for materials, products, systems, and services — including polygraph instrumentation and practice. ASTM standards define the scientific term "Psychophysiological Detection of Deception" (PDD) used in federal polygraph contexts.
Attention Physiology
The focusing or concentration of mental activity on a stimulus. Central to the theory of salience in polygraph testing — the most salient (personally relevant or threatening) question captures the examinee's attention and produces the strongest physiological response. The modern scientific framework for understanding differential arousal in comparison question techniques.
autogenic training Techniques
Autogenic training is a form of self-hypnosis in which individuals learn to induce a state of profound relaxation through simple exercises. Because it can help modify physiological arousal, it has been discussed as a potential countermeasure against polygraph testing.
automatic mode Techniques
Automatic mode (also labelled Auto, Auto-Centre, or Auto EDA) is a setting on the polygraph's electrodermal activity channel that uses a combination of filtering — including low-pass, high-pass, and smoothing filters — to keep the electrodermal tracing centred on the display.
The part of the nervous system that controls involuntary physiological functions including heart rate, blood pressure, respiration, and sweat gland activity. The ANS is the biological basis for polygraph testing — deception creates cognitive and emotional arousal that triggers measurable ANS responses. Divided into the sympathetic (arousal) and parasympathetic (calming) branches.
AVATAR Techniques
AVATAR — Automated Virtual Agent for Truth Assessment in Real-time — is an experimental multi-sensor deception detection platform designed for border crossings and airports. Unlike the traditional polygraph, AVATAR operates as an automated screening tool that can process large numbers of individu...
Axciton Systems Instruments
A manufacturer of computerised polygraph instruments used in government and law enforcement settings. Axciton systems integrate digital data acquisition with built-in scoring algorithms for real-time physiological monitoring during lie detector tests.
axon Physiology
An axon is the long central process of a neuron responsible for transmitting nerve impulses from the cell body to the synapse or target organ. In humans, most peripheral axons are insulated by a fatty layer called myelin, with regular breaks (nodes of Ranvier) that allow electrical impulses to ju...
B
One of the earliest structured Comparison Question Test (CQT) formats, developed by Cleve Backster in the 1960s. Introduced the concept of dividing questions into "zones" and pairing specific relevant questions with specific comparison questions. The foundation for modern Zone Comparison Test (ZCT) formats used by federal agencies.
One of the most influential pioneers in the field of polygraph testing. Developed the Zone Comparison Test (ZCT), introduced the concepts of psychological set, zones, spots, superdampening, anti-climax dampening, symptomatic questions, exclusionary comparison questions, and 7-position numerical scoring. Founded the CIA polygraph program in 1949 and operated a private training school in San Diego for decades.
Base Rate Scoring
The incidence or prevalence of deception in a tested population, expressed as a proportion. Base rates affect the confidence in polygraph decisions — detection is significantly easier when the base rate of deception is higher (e.g., 50%) than in low base rate conditions (e.g., 1%).
The normal physiological state of an examinee established at the beginning of a polygraph examination using neutral or irrelevant questions. All subsequent physiological responses are compared against this baseline to identify significant deviations that may indicate deception. Accurate baseline establishment is critical to polygraph testing reliability.
Baseline Arousal Physiology
A marked upward shift in the entire breathing tracing during a polygraph examination. While not exclusively associated with deception, baseline arousals are considered reliable indicators of stress when observed. They may last from a few breathing cycles to sustained elevation.
Bayesian Analysis Scoring
A statistical approach used in polygraph scoring algorithms (including PolyScore) that calculates the posterior probability of deception given the observed physiological data and prior base rate information. Bayesian methods allow polygraph results to be expressed as probability estimates rather than simple binary classifications, providing more nuanced diagnostic information.
Behavioral Observation Practice
The examiner's assessment of the examinee's non-verbal behaviour, verbal responses, and demeanour during the polygraph examination. While some historical techniques relied heavily on behavioural cues, APA standards now emphasise that diagnostic opinions must be based solely on physiological data analysis using validated scoring methods — not on behavioural impressions alone.
Benussi, Vittorio Practice
Vittorio Benussi (1878–1927) was one of the earliest researchers to examine breathing tracings for detecting deception. Though Italian, Benussi conducted most of his work at the University of Graz in Austria.
Berkeley psychograph Instruments
The Berkeley psychograph (also called the Lee Polygraph) was a two-channel polygraph with an event marker, assembled by C.D. Lee of Berkeley, California. It included a pneumograph and cardiograph, recording both channels simultaneously on moving graph paper. Designed to be as portable as a suitca...
beta blocker Practice
A beta blocker is a class of medication that blocks the effects of adrenaline on the cardiovascular system. Beta blockers are prescribed for high blood pressure, arrhythmias, and other cardiac conditions.
bias Practice
Bias is a source of systematic error that can influence experimental outcomes. In polygraph research, bias can be introduced through non-random sampling, faulty instructions to subjects, or researcher expectations.
Biofeedback Physiology
A technique in which an individual receives real-time information about their own physiological processes. In polygraph contexts, biofeedback has been studied both as a potential countermeasure concern and as a method to enhance examinee responsiveness during testing. Some research suggests immediate biofeedback may elicit greater physiological responding to deception.
bizone Techniques
Bizone is an incorrect term sometimes applied to a Zone Comparison Test containing only two relevant questions. The term \"zone\" in polygraph terminology refers to a block of chart time initiated by a specific question type — not to the number of relevant questions. A test with two relevant questi...
Black Zone Techniques
In Backster's Zone Comparison Test, the portion of the question sequence containing symptomatic (outside-issue) questions. Designed to identify examinee concerns about issues outside the scope of the test. Distinguished from the Red Zone (relevant questions) and Green Zone (comparison questions). The diagnostic value of the Black Zone has been debated in research.
blind chart analysis Scoring
Blind chart analysis is the evaluation of polygraph recordings without the benefit of extra-polygraphic information such as examinee behaviour, case facts, pre-test admissions, or base rates of deception. Studies employ various degrees of \"blindness.\"
A quality control method where a second examiner scores polygraph charts without knowledge of the original examiner's findings, case facts, pre-test admissions, or behavioural observations. Blind review is a popular research approach to gauge interrater reliability and is considered the most objective form of quality control. Various degrees of "blindness" are employed in research and field practice.
blind stimulation test Techniques
A blind stimulation test is a stimulation test in which the examiner does not know the critical item at the beginning of the test. The examinee selects a number, card, or other item, and the examiner attempts to identify it from the physiological responses — demonstrating to the examinee that the...
Blocking Physiology
A respiratory pattern observed in polygraph tracings characterised by the examinee holding their breath at or near the inspiratory peak (top of the breath). Distinguished from apnea, which typically occurs at the expiratory segment. Blocking is frequently a deliberate countermeasure attempt to distort respiratory data and is flagged by trained examiners during chart analysis.
One of the primary physiological channels recorded during a polygraph examination. Measured via a blood pressure cuff (cardio cuff) on the upper arm. The polygraph records changes in relative blood pressure, pulse rate, and pulse amplitude in response to test questions.
A measurement of blood volume changes in peripheral blood vessels, typically recorded from the fingertip using a plethysmograph sensor. BVP data provides information about pulse rate, pulse amplitude, and vasoconstriction patterns. Used as a supplementary physiological channel in some modern polygraph instruments alongside the standard cardio cuff.
bogus pipeline Theory
The bogus pipeline (BPL) is a sociopsychological phenomenon where individuals make more candid disclosures when they believe a device can detect their true knowledge or attitudes. First documented by Jones & Sigall (1971), subjects attached to what they believed was a sensitive measuring instrume...
Bootstrap Method Scoring
A resampling statistical technique used in polygraph research to estimate confidence intervals and sampling distributions from field examination data. The bootstrap method generates thousands of simulated samples by randomly drawing with replacement from the original dataset. Extensively used in the development and validation of OSS-3 cut-scores and decision rules.
bootstrapping Scoring
Bootstrapping is a statistical technique that involves pooling data from two samples, drawing repeated random samples with replacement to create a distribution, and then using that distribution to determine whether the original samples are significantly different. The number of resamplings is typ...
The United Kingdom's professional body for polygraph examiners. Maintains a register of qualified practitioners, sets standards for UK-based polygraph testing, and adapts APA terminology and standards for British practice.
brachial artery Physiology
The brachial artery is the major blood vessel in the upper arm. It is the preferred placement site for the blood pressure cuff in polygraph testing, where occlusion sensors are placed to record relative changes in blood pressure and the arterial pulse wave.
bradycardia Physiology
Bradycardia is a heart rate below 60 beats per minute. It is common among athletes and individuals with hypothyroidism, and can also indicate medication effects. In polygraph testing, bradycardia is noted during the Pre-Test Interview and medical history review, as it may influence the interpreta...
bradypnea Physiology
Bradypnea is abnormally slow breathing with prolonged cycle times. The term does not distinguish between autonomic slowing and deliberate breathing manipulation. In polygraph testing, bradypnea may be observed as a natural physiological pattern or may indicate potential countermeasure activity by...
brain stem Physiology
The brain stem includes the midbrain, pons, and medulla oblongata, along with structures such as the thalamus, third ventricle, and hypothalamus. These structures are essential for the automatic control of respiration and cardiovascular function.
breakdown test Techniques
A breakdown test (also called a breakout test) is a single-issue PDD test administered after a multiple-issue screening examination has identified a specific area of concern. It is conducted using one of the validated test formats, such as a Zone Comparison Test or AFMGQT.
breathing Physiology
Breathing (also called respiration) is one of the standard physiological signals recorded in PDD testing. Respiratory data are obtained via Pneumograph transducers placed around the thorax and abdomen.
Brilograf Instruments
The Brilograf was a device for measuring changes in skin resistance, built in the 1940s by criminologist Jacques Bril. Based on work Bril had done with Rev. Walter Summers on the Pathometer, the Brilograf was not widely used and is primarily of historical interest in the development of electroder...
British One-issue Screening Test Techniques
The British One-issue Screening Test (BOST) is a polygraph format developed as a variation of the Air Force Modified General Question Test, designed specifically for single-issue screening. The BOST was created to serve programmes in the United Kingdom such as Post-Conviction Sex Offender Testing.
C
Calibration Verification of Sensitivity Test Techniques
The Calibration Verification of Sensitivity Test (CVOS) is a testing procedure conducted as the first chart of a polygraph examination. It assesses the examinee's capability to process information, helps detect countermeasures, permits adjustment of instrument gain settings, verifies sufficient r...
card test Techniques
The card test is a type of stimulation test in which the examinee selects a card from a deck and is then tested on the number, letter, or character on the card. While widely used in early polygraph practice, it has been largely replaced by other stimulation methods.
A blood pressure cuff placed on the examinee's upper arm during a polygraph test. Records cardiovascular data including relative blood pressure changes, pulse rate, and pulse amplitude. One of the four primary physiological channels in modern lie detector testing.
cardio-pneumo-psychograph Instruments
The cardio-pneumo-psychograph was a two-channel polygraph developed by John Larson in the 1920s for use in criminal investigations. Recording both cardiovascular and respiratory data simultaneously, it was one of the earliest instruments to qualify as a true polygraph.
cardioactivity monitor Instruments
The cardioactivity monitor (CAM) is a cardiovascular sensor placed on the fingertip or thumb that detects changes in distal blood volume via strain gauge sensors attached to a metal diaphragm. It provides an alternative to the traditional blood pressure cuff but is used less frequently in practice.
cardiograph Instruments
A cardiograph is a general term for any recording of heart activity. In PDD, the use of a blood pressure cuff to monitor relative arterial blood pressure changes and pulse wave is more precisely described as sphygmography or occlusion plethysmography, though \"cardiograph\" remains the common term ...
cardiosphygmograph Instruments
The cardiosphygmograph is an alternate term for the pulse wave and relative blood pressure tracing in PDD. Common in polygraph literature from the 1930s through 1950s, it is more precise than the current shorthand \"cardiograph\" or \"cardio\" but is rarely used today.
cardiotachometer Instruments
A cardiotachometer is an instrument that measures heart rate. Since heart rate can only be accurately measured over several seconds, real-time displays typically show the inter-beat interval converted into its reciprocal to give cardiac rate.
catacrotic limb Physiology
The catacrotic limb is the descending (downward) portion of an arterial pulse wave in the cardiograph tracing. It represents the relaxation phase (diastole) of the cardiac cycle, when ventricular pressure decreases and the pulse wave declines. The Dicrotic Notch appears on the catacrotic limb.
category bar Techniques
A category bar is a technique in polygraph question construction that restricts the scope of a Comparison Question so it covers a different category of behaviour from the Relevant Question. For example, if the relevant question concerns theft, a category-barred comparison might address dishonesty...
central nervous system Physiology
The central nervous system (CNS) consists of the brain and spinal cord. While closely integrated with the Autonomic Nervous System, CNS activity is not separately measured in traditional polygraph testing. However, CNS measures such as event-related potentials have been used experimentally in Con...
Credits earned through approved training, seminars, conferences, peer-reviewed publications, or university courses. APA members must complete a minimum of 30 CEU hours every two years to maintain membership and accreditation. CEUs ensure examiners stay current with evolving polygraph testing techniques and standards.
The recorded output of a single presentation of all test questions during a polygraph examination. A complete exam typically includes 3–5 charts (also called chart series). Each chart captures simultaneous physiological data across all channels (respiration, EDA, cardiovascular, and movement) for the full question sequence.
chart identification Practice
Chart identification refers to the administrative information annotated on a polygraph chart by the examiner: date, time, test number, examiner name, case number, signatures, and other details required by the polygraph programme. Not to be confused with chart markings.
chart markings Practice
Chart markings are annotations on the physiological tracings that denote question onset and offset, the examinee's answer, question number, question type, artifacts, and other details important for interpreting the physiological data.
Cheyne-Stokes respiration Physiology
Cheyne-Stokes respiration is a pattern of cyclical variation in breathing amplitude, sometimes interspersed with periods of Apnea. This pattern is typically associated with brain damage, congestive heart failure, kidney disease, or drug abuse. Its appearance during polygraph testing would indicat...
chi-square test Scoring
The chi-square test (χ²) is a non-parametric inferential statistical test used to evaluate relationships between categorical variables — such as comparing groups of polygraph test outcomes (deceptive vs. truthful vs. inconclusive). It lacks the sensitivity of other methods and is primarily used i...
Child Custody Testing Practice
Polygraph examinations used to establish parental fitness or address specific allegations in custody disputes. Typically addresses concerns such as abuse, neglect, substance use, or other fitness-related issues. Requires particular sensitivity and strict adherence to APA ethical standards given the high-stakes family law context.
cholinergic Physiology
Cholinergic describes neurons that release the neurotransmitter acetylcholine. In polygraph science, the term is important because the sympathetic nerves to the eccrine sweat glands — which produce the electrodermal activity measured by the polygraph — are unusually cholinergic rather than adrene...
classical conditioning Techniques
Classical conditioning is the process of establishing a response to a stimulus that does not normally evoke that response, first described by Ivan Pavlov. In polygraph theory, it is possible that conditioned physiological responses occur uniquely during deception — making classical conditioning o...
clearing chart Techniques
A clearing chart is typically a Relevant/Irrelevant screening test administered after a breakdown test, covering the remaining relevant questions not addressed in the breakdown. In field practice it normally involves a single chart.
clinical approach Techniques
The clinical approach (also called global analysis) is an assessment technique in PDD that includes extra-polygraphic information — such as case facts, examinee behaviour, and base rates — in arriving at a conclusion. This contrasts with the purely numerical approach, which bases decisions exclus...
closed-eyes technique Techniques
The closed-eyes technique is a polygraph examination procedure in which the examinee is instructed to keep their eyes closed during testing. Used by a minority of PDD examiners, the effects of open versus closed eyes on physiological responding have not been thoroughly investigated.
Cognitive Load Physiology
The mental effort required to perform a task, such as constructing and maintaining a deceptive narrative during a polygraph examination. Deception is theorised to impose greater cognitive load than truth-telling because the examinee must simultaneously suppress the truth, fabricate a response, and monitor the plausibility of their statements — all of which produce measurable physiological changes.
community safety examinations Techniques
Community safety examinations are a broad category of polygraph tests designed to detect and deter illegal behaviours that jeopardise public safety. They include Post-Conviction Sex Offender Testing, Domestic Violence Offender Testing (DVOT), and Intoxicated Drivers on Probation (IDOP) programmes.
comparative response question Practice
The comparative response question is the original name given by John Reid in 1947 for what would later be called the control question and ultimately the Comparison Question. It was a probable-lie question designed to elicit responses for comparison against relevant question responses.
A question in a polygraph test designed to elicit a physiological response from truthful examinees. Comparison questions are typically broad, emotionally provocative questions about past behaviour (e.g., "Have you ever lied to someone who trusted you?"). Responses to comparison questions are compared with responses to relevant questions to determine deception.
comparison/control question validation test Techniques
The comparison/control question validation test is a procedure in which probable-lie comparison questions are tested against relevant questions from a contrived crime to verify that the examinee will respond to the comparison questions. Proposed by James Matte for use in his Quadri-Track Techniqu...
Compliance Testing Practice
A polygraph examination used to verify that an individual is adhering to specific conditions or agreements, such as probation terms, treatment requirements, or workplace policies. Most commonly used in PCSOT programs to monitor sex offender compliance with supervision conditions. Results are typically reported using screening terminology (SR/NSR).
Computer Assisted Polygraph System Techniques
The Computer Assisted Polygraph System (CAPS) was developed by David Raskin and John Kircher at the University of Utah. It interfaced modified analog polygraphs with a computer, using discriminant analysis to weigh and combine physiological measurements and calculate the probability of deception....
A polygraph technique that tests whether an examinee possesses knowledge of specific details about an event or crime that only a guilty person would know. Also known as the Guilty Knowledge Test (GKT). Uses multiple-choice question formats where only one option contains the crime-relevant detail. Widely used in Japan and in research settings.
conditional probabilities Scoring
Conditional probabilities express the likelihood of an event given a set of conditions — written as p(A|B): \"what is the probability of A given B?\" In PDD, this concept is critical for understanding Accuracy. A False Negative can be expressed as: p(no deception indicated | the person is actually ...
conditioned response theory Theory
Conditioned response theory holds that polygraph responses result from emotional reactions triggered by conditioned stimuli. When a stimulus is associated with strong emotions, larger physiological responses are expected. While there is support for this — responding correlates with the personal s...
The measure of the skin's ability to conduct electrical current, which increases with sweat gland activity. Measured in microsiemens (μS) through finger electrodes during a polygraph test. Higher conductance values indicate greater sympathetic nervous system arousal. Skin conductance is the inverse of skin resistance and is the preferred measurement unit in modern EDA recording.
confabulation Theory
Confabulation is the reporting of imagined experiences as genuine memories, without conscious intent to deceive. It can result from organic brain disorders or developmental factors. Confabulation is relevant to PDD because an examinee who genuinely believes a false memory is not engaging in delib...
A voluntary disclosure by the examinee during or after a polygraph examination acknowledging involvement in, or knowledge of, the matter under investigation. Confessions may be elicited during the post-test interview when results indicate deception. APA standards require that confessions be obtained without coercion and that examinees retain all legal rights throughout the process.
Confidentiality Practice
The ethical and legal obligation of the polygraph examiner to protect the privacy of examination results and examinee information. APA standards require that results be disclosed only to authorised parties as specified in the informed consent agreement. Violations of confidentiality may result in APA disciplinary action and legal liability.
confirmatory testing Techniques
Confirmatory testing is a PDD examination used to verify the statements of witnesses, victims, or confidential sources. Unlike investigative examinations that seek to uncover deception, confirmatory tests aim to corroborate information already provided.
Confirmed Case Techniques
A polygraph examination where the ground truth (whether the examinee was genuinely deceptive or truthful) has been independently verified through confessions, physical evidence, DNA, or other conclusive means. Confirmed cases are essential for polygraph validation research because they provide the criterion against which scoring accuracy is measured. Also called criterion cases.
conflict theory Theory
Conflict theory proposes that the simultaneous activation of conflicting motivations — the desire to lie versus the desire to tell the truth — produces physiological arousal. The greater the internal conflict, the larger the response. Originating from Aleksandr Luria's work in the 1920s–1930s, it...
conspecnificance Scoring
Conspecnificance is a mnemonic device used in PDD training standing for consistency, specificity, and significance — three characteristics a physiological response must exhibit to support a finding of deception. Responses must appear regularly to the same questions, manifest uniquely to those que...
constant current method Scoring
The constant current method is a technique for measuring skin resistance in which the electrical current applied to the skin is held constant while changes in resistance are recorded. It is one of two exosomatic approaches to electrodermal measurement, the other being the constant voltage method.
constant voltage method Scoring
The constant voltage method measures skin conductance by holding the voltage applied to the skin constant while recording changes in conductance. Modern computerised polygraphs typically use this approach, measuring electrodermal activity in units of conductance (Siemens or microSiemens).
containment approach Practice
The containment approach is a collaborative framework in which the criminal justice system, treatment providers, and polygraph examiners work as a team, sharing information equally. Originally developed for managing sex offenders, containment teams may also include child protective services, pros...
control group Practice
In research, the control group differs from the experimental group only in that it does not receive the treatment or manipulation being studied. In PDD research, the control group is typically the \"innocent\" group that did not commit the mock crime, providing a baseline against which \"guilty\" (ex...
control question Practice
Control question is a superseded term now replaced by Comparison Question. The name \"control\" traced back to the 1930s and stimulation tests used as \"controls\" for comparison with relevant question responses. In 1947, John Reid published a paper using the term, and it became standard for nearly 5...
control test Techniques
A control test is an alternate term for a known-numbers test. See: stimulation test.
correlation Scoring
Correlation measures how one variable changes with another, ranging from -1.00 (perfect negative) to +1.00 (perfect positive), with 0.00 indicating no linear relationship. In PDD research, correlation is used to assess relationships such as scoring ability versus experience, or the relationship b...
cortisol Physiology
Cortisol is a steroid hormone produced by the adrenal cortex in response to stress. It replenishes energy stores depleted during acute stress responses by converting food sources into storage forms such as glycogen or fat. In PDD research, cortisol is studied as a physiological marker of the stre...
Countermeasures Practice
Deliberate physical or mental actions taken by an examinee to manipulate polygraph test results. Physical countermeasures include controlled breathing, muscle tension, tongue biting, or toe pressing. Mental countermeasures include counting, mental imagery, or dissociation. Modern polygraph instruments use activity sensors and examiner observation to detect countermeasure attempts.
A computerised scoring system developed by Scientific Assessment Technologies based on University of Utah research. Automates the scoring process by applying statistical classification algorithms to digitised polygraph data, reducing subjective interpretation and improving inter-rater reliability.
The most widely used polygraph testing format worldwide. Compares physiological responses to relevant questions (about the issue under investigation) against responses to comparison questions (broader questions about past behaviour). APA-validated variants include the Utah CQT, Federal ZCT, and Backster technique. Forms the basis of most diagnostic polygraph testing.
craniosacral division Physiology
The craniosacral division is an anatomical classification of the parasympathetic branch of the Autonomic Nervous System. It represents the sites where parasympathetic nerves exit the central nervous system — through some cranial nerves and sacral spinal nerves. This division is involved in the co...
Credibility Assessment Practice
An umbrella term for the multi-disciplinary field that relies on physiological and behavioural measures to test the agreement between an individual's memories and statements. Credibility assessment approaches include reaction time tests, word association tests, polygraph, central nervous system measures (such as EEG and fMRI), behavioural analysis, and ocular technologies like EyeDetect.
Criterion Accuracy Scoring
The percentage of correct polygraph decisions when measured against independently confirmed ground truth. Criterion accuracy is calculated separately for deceptive cases (sensitivity) and truthful cases (specificity). APA meta-analyses report criterion accuracy rates exceeding 86% for validated techniques using approved scoring methods, with some algorithms exceeding 90%.
critical item Practice
In Peak of Tension or Concealed Information Test formats, the critical item is the stimulus that guilty persons recognise as related to the event of interest. It is embedded among irrelevant items that all appear equally plausible to an innocent examinee. Sometimes called a \"key.\"
Cross-Validation Scoring
A statistical method used to evaluate how well a polygraph scoring algorithm will generalise to independent data sets. Involves training the algorithm on one sample of confirmed cases and testing it on a separate sample. Essential for preventing overfitting and establishing genuine predictive accuracy. The National Academy of Sciences (2003) emphasised that proper cross-validation is critical for all polygraph scoring systems.
A screening polygraph examination focused specifically on counterintelligence issues including espionage, sabotage, and unauthorised disclosure of classified information. Commonly used for U.S. government security clearance vetting. A subset of the Full-Scope (Lifestyle) polygraph which covers additional personal conduct areas.
A current exclusive comparison question is an exclusionary probable-lie comparison question whose scope includes the time period of the relevant issue but is excluded from the relevant issue by category, place, or another delimiter. See: Matte (1996).
The numerical boundary in a scoring system that separates deceptive from non-deceptive classifications. Scores above the positive cut-score indicate truthfulness (NDI); scores below the negative cut-score indicate deception (DI); scores between the two are classified as inconclusive. Cut-scores are empirically derived from validated research samples and directly affect the balance of sensitivity, specificity, and inconclusive rates.
A device that claims to detect deception by analysing microtremors in the human voice. Marketed as an alternative to polygraph testing. Independent peer-reviewed research has consistently failed to validate CVSA accuracy as a reliable lie detection method. Not endorsed by the APA or any recognised scientific body. See also VSA.
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Daubert Standard Legal
The legal standard for admissibility of scientific evidence in U.S. federal courts, established by Daubert v. Merrell Dow Pharmaceuticals (1993). Replaced the older Frye standard. Requires that scientific evidence be testable, peer-reviewed, have a known error rate, and be generally accepted. Polygraph advocates argue that modern validated techniques meet the Daubert criteria; courts remain divided on admissibility.
The Daubert case (1993) set aside the Frye Rule's \"general acceptability\" standard for admitting scientific evidence in favour of the Federal Rules of Evidence. The judge acts as gatekeeper, evaluating whether evidence is based on scientific knowledge that is testable, peer-reviewed, has known er...
deception Practice
Deception is the deliberate act of providing or omitting information with the intention of misleading. The critical element is intent — without intent to mislead, deception does not occur regardless of the information's accuracy.
deception exemplar Practice
A deception exemplar is a physiological response pattern that the examinee expects to serve as a sample of what occurs when they are being deceptive, used for comparison against responses to relevant questions. The concept is associated with stimulation tests that demonstrate the polygraph's abil...
deception test Theory
A deception test is a polygraph format that asks directly about the matter under investigation and can address multiple behavioural issues. The two broad categories are the Relevant/Irrelevant technique and the Comparison Question Technique. The term contrasts with \"recognition test,\" which asses...
Defensible Dozen Scoring
A mnemonic term for the approximately twelve validated physiological features used in polygraph chart interpretation. Includes four respiratory features (suppression, apnea, slowing, baseline rise), three electrodermal features (amplitude, duration, complexity), three cardiovascular features (baseline rise, duration, pulse amplitude increase), and one vasomotor feature (constriction). These features have replicated scientific support.
degrees of freedom Scoring
Degrees of freedom (df) is a statistical concept referring to the number of independent observations minus the number of parameters being estimated. In any data set, all values can be freely selected except the last, which is determined. Degrees of freedom are essential for calculating significan...
delayed answer test Techniques
The delayed answer test (DAT) is an experimental methodology that demonstrated physiological arousal is more closely tied to the presentation of the stimulus (the question) than to the act of giving a deceptive answer. This finding supports the view that polygraph responses are triggered by cogni...
dendrite Physiology
A dendrite is a branching process of a neuron specialised to receive incoming signals from other neurons. Dendrites function as the postsynaptic receptor region, collecting information that the neuron integrates before potentially transmitting a signal along its axon. In the context of PDD, dendr...
dependent variable Scoring
A dependent variable changes as a result of the experimenter's manipulation of the independent variable. In PDD research, electrodermal activity could serve as a dependent variable that changes in response to stimulus intensity (the independent variable). Identifying and controlling variables is ...
A diagnostic opinion indicating that physiological data from the polygraph examination suggests the examinee was deceptive in response to one or more relevant test questions. DI is used in single-issue (specific) testing only — not in screening examinations, which use SR/NSR terminology instead.
Diagnostic and Statistical Manual Practice
The Diagnostic and Statistical Manual of Mental Disorders (DSM) is the official classification system for psychiatric and psychological disorders in the United States, published by the American Psychiatric Association. The current edition is the DSM-5 (2013). It is relevant to PDD because certain...
Diagnostic Opinion Results
The examiner's professional judgment regarding the truthfulness of an examinee based on physiological data analysis. Diagnostic opinions in single-issue testing include DI (Deception Indicated), NDI (No Deception Indicated), or INC (Inconclusive). Based solely on validated scoring methods and physiological evidence, not behavioural observation.
diastole Physiology
Diastole is the phase of the heartbeat cycle when the heart muscles relax and the chambers fill with blood. In the polygraph's cardiograph tracing, left ventricular diastole is represented by the descending limb (catacrotic limb) of the pulse wave.
diastolic blood pressure Physiology
Diastolic blood pressure is the lowest blood pressure value occurring during the relaxation phase of the cardiac cycle. Combined with systolic pressure, it provides context for the cardiovascular changes observed during polygraph testing.
dichotomization theory Theory
Dichotomization theory hypothesises that Habituation rates differ for responses to relevant and comparison questions. Guilty subjects supposedly habituate more slowly to relevant questions, while innocent examinees continue responding more strongly to comparison questions over time. The theory ha...
dichotomous variables Scoring
Dichotomous variables are those with only two mutually exclusive and exhaustive possibilities: yes/no, deceptive/truthful, 0/1. In PDD, the fundamental outcome is dichotomous — the examinee is either truthful or deceptive to the relevant issue.
Dicrotic Notch Physiology
A small downward deflection visible in the cardiovascular polygraph tracing that occurs when the aortic valve closes at the end of systole. The presence and clarity of the dicrotic notch is an indicator of cardiovascular signal quality. Absence or distortion may suggest an improperly fitted cardio cuff or medical conditions affecting the examinee's cardiovascular system.
differential responsivity Physiology
Differential responsivity refers to the differences in physiological responses between question types. In CQT formats, it relates to the relative response magnitudes from relevant versus comparison questions. This differential pattern persists even when overall responsivity is attenuated, which i...
Modern polygraph instruments that convert physiological signals to digital data in real-time, displayed on a computer screen. Replaced analog (paper) instruments in the early 2000s. Digital systems enable automated scoring algorithms, electronic data storage, precise measurement, and real-time quality monitoring. All major manufacturers (Lafayette, Limestone, Stoelting, Axciton) now produce digital instruments exclusively.
A type of comparison question where the examinee is instructed to answer "No" to a question they know to be false (e.g., "During the first 20 years of your life, did you ever tell even one lie?"). Provides a known deceptive response as a physiological comparison baseline. Considered more standardised than probable-lie comparison questions.
Disclosure Test Practice
A polygraph examination format used to verify the completeness and accuracy of an examinee's written disclosure statement, particularly in PCSOT and treatment contexts. The examinee prepares a comprehensive written account, and the polygraph test addresses whether the disclosure omits significant information. Commonly used in sex offender treatment programs.
Discriminant Analysis Scoring
A statistical classification method used in several polygraph scoring algorithms (including PolyScore and CPS) to separate deceptive from truthful examinees based on weighted combinations of physiological response features. The algorithm identifies which combination of variables (Kircher features) best discriminates between the two groups. Also known as Linear Discriminant Analysis (LDA).
dissociation Practice
Dissociation in PDD refers to the deliberate mental disengagement of an examinee from the testing situation — a form of mental countermeasure. Examinees using this tactic hope to eliminate physiological responding by mentally distancing themselves from the test questions.
A polygraph screening format used primarily for pre-employment and security vetting. Test issues may include criminal history, drug use, theft from previous employers, domestic abuse, and application falsification. Requires the examinee to intentionally lie to certain questions for comparison purposes. An APA-validated technique when scored with approved TDA methods.
A Comparison Question Test format that uses directed-lie comparison questions (where the examinee is explicitly instructed to lie). The DLT is considered more standardised and ethically transparent than probable-lie formats because the examinee is told to lie rather than being manipulated into doing so. Research shows comparable or superior accuracy to probable-lie methods. APA-validated.
The former name of the U.S. federal polygraph training and research centre, now known as the National Center for Credibility Assessment (NCCA). Located at Fort Jackson, South Carolina. Responsible for training all federal government polygraph examiners (except CIA and NSA) and conducting foundational polygraph research. See NCCA.
A polygraph examination used to help resolve personal issues between individuals in a romantic or sexual relationship. May address concerns about infidelity, sexual contact, financial deception, or other trust-related matters. One of the most common categories of private lie detector testing. See our polygraph pricing guide for current rates.
domestic violence offender testing Techniques
Domestic violence offender testing (DVOT) is a polygraph programme monitoring convicted domestic violence offenders on probation or parole. Like PCSOT, it uses the polygraph to verify compliance with release conditions and deter future violence, contributing to community safety through detection ...
double verification test Techniques
The double verification test is an alternate term for the card test. See: stimulation test.
Dual Process Theory Physiology
A cognitive framework proposing that deception involves two competing mental processes: an automatic truth response that must be actively suppressed, and a controlled deceptive response that must be deliberately constructed. This dual processing creates measurable cognitive load and physiological arousal that polygraph instruments are designed to detect.
dyspnea Physiology
Dyspnea is laboured or difficult breathing, generally resulting from disease or a medical condition. In polygraph testing, dyspnea observed in the respiratory tracings may indicate an underlying health condition rather than a response to test questions, and the examiner must distinguish it from d...
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Easterbrook Hypothesis Theory
The Easterbrook Hypothesis proposes that attentional resources become more restricted as the level of arousal increases. Under high arousal, peripheral stimuli receive less processing while attention narrows to the most salient features of the environment.
eccrine glands Physiology
Eccrine glands are one of two types of sweat glands in the human body. Found throughout the skin but in highest concentration on the hands and feet, eccrine glands are responsible for the electrodermal activity measured by the polygraph. Their activity is controlled by cholinergic sympathetic ner...
Eccrine Sweat Glands Physiology
Sweat glands found primarily on the palms, fingertips, and soles of the feet that are innervated by the sympathetic nervous system and respond to emotional stimuli rather than thermoregulation. Eccrine gland activity on the fingertips produces the electrodermal changes measured by the polygraph's EDA sensors. The density of eccrine glands on the fingers makes them the optimal placement site for EDA electrodes.
A comparison question format introduced by Backster that explicitly excludes the time period and subject matter of the offence under investigation (e.g., "Before 2020, did you ever take anything that didn't belong to you?"). Designed to prevent deceptive examinees from confusing relevant and comparison question responses. Contrasts with the Non-Exclusive Comparison Question (NECQ) used in the Reid technique.
Measurement of electrical conductance changes in the skin caused by sweat gland activity, recorded via finger plates (electrodes) during a polygraph test. Also historically known as GSR (Galvanic Skin Response) or EDR (Electrodermal Response). EDA is considered the most diagnostically powerful single channel in polygraph testing, showing the highest correlation with deception.
Effect Size Scoring
A statistical measure of the magnitude of difference between physiological responses to relevant versus comparison questions. Larger effect sizes indicate clearer physiological discrimination between question types. Effect sizes are used in polygraph validation research to compare the diagnostic power of different techniques and scoring methods across studies.
efferent nerves Physiology
Efferent nerves (also called motor nerves) carry impulses from the central nervous system to muscles and effector organs. In PDD, the efferent pathways of the Autonomic Nervous System transmit the signals that produce the measurable physiological changes recorded by the polygraph — changes in hea...
Either-Or Rule Scoring
The Either-Or Rule is a scoring rule developed by Cleve Backster used exclusively in the Backster Zone Comparison Technique. If a Relevant Question does not evoke a physiological reaction, it is scored against the adjacent Comparison Question with the larger reaction. If the relevant question doe...
electrocardiogram Instruments
An electrocardiogram is a recording of the heart's electrical activity, consisting of P, Q, R, S, T, and U waves. While ECG data have not proven directly diagnostic for PDD, research on the pre-ejection period (derived from ECG and impedance cardiography) and inter-beat intervals has shown promis...
electrodermal response Physiology
An electrodermal response (EDR) is a skin reaction measured by changes in its electrical properties, including skin resistance (SR), skin conductance (SC), and skin potential (SP). The EDR is one of the most diagnostic physiological measures in PDD testing, as sweat gland activity closely correla...
electroencephalogram Instruments
An electroencephalogram (EEG) records the brain's electrical activity generated by clusters of neurons. In recent years, EEG methodology has been applied to deception detection through event-related potentials and Concealed Information Test paradigms. EEG-based approaches are attractive because c...
electrooculograph Instruments
An electrooculograph records electrical activity produced during eye movements. In deception testing, EOGs have been used as deception indicators (lateral eye movements carry diagnostic information) and as artifact correction tools for brain wave research, where eye movement signals can interfere...
embarrassing personal question Practice
The embarrassing personal question (EPQ) was a question type — frequently with a sexual theme — used by Leonarde Keeler with the Relevant/Irrelevant test in the late 1940s and early 1950s. Keeler hypothesised that guilty subjects would not respond to it (remaining focused on relevant questions), ...
A technique for measuring electrical activity produced by skeletal muscles. While not a standard polygraph channel, EMG has been investigated as an additional physiological measure for detecting physical countermeasure attempts (e.g., subtle muscle tensing). Some advanced polygraph instruments incorporate EMG sensors in the activity monitoring system.
emotional standard Practice
The emotional standard is a term coined by Rev. Walter Summers for an emotion-provoking question to which the examinee answers truthfully but would prefer to conceal. Its reaction was compared against relevant question responses. This is the earliest documented use of what would later become the ...
empirical Practice
Empirical describes an approach based entirely on observation and data rather than speculation or theory. Much of PDD research is empirical — testing polygraph accuracy through controlled experiments rather than relying on theoretical predictions alone. The shift toward empirical, evidence-based ...
endosomatic Physiology
Endosomatic refers to electrical signals generated from within the body itself. In electrodermal measurement, the endosomatic approach records skin potential (SP) — voltage generated by the dermis without applying external current. EEG and ECG signals are also endosomatic. This contrasts with exo...
The professional body promoting polygraph standards and scientific research across European member countries. Hosts annual conferences, publishes research, and maintains ethical guidelines for European polygraph practice.
epinephrine Physiology
Epinephrine (called adrenaline in British usage) is a hormone that stimulates the sympathetic nervous system. It constricts peripheral blood flow, raises blood pressure, increases cardiac activity, releases glucose, and inhibits digestion. These physiological changes are among those the polygraph...
A U.S. federal law that prohibits most private-sector employers from requiring, requesting, or using lie detector test results as a condition of employment. Exemptions apply to federal, state, and local government employers, certain security-related industries, and investigations involving economic loss or injury. Violations carry civil penalties up to $10,000. See our complete EPPA guide for detailed information.
An APA-validated scoring system using a three-position scoring model with empirically derived decision rules. ESS uses a "bigger-is-better" approach with electrodermal weighting and two-stage decision rules (Grand Total Rule + Spot-Score Rule). Research demonstrates accuracy rates exceeding 90% with experienced and inexperienced scorers alike. Free and open-source.
A pre-test evaluation to determine whether an examinee is physically, psychologically, and medically suitable for a polygraph examination. Factors assessed include medication use, medical conditions, cognitive capacity, pregnancy, extreme fatigue, or substance intoxication. An unsuitable examinee should not be tested.
A computer-automated version of the manual Empirical Scoring System (ESS), implemented in Limestone Technologies polygraph instruments. Uses automated Kircher feature measurements and regression-derived weightings for multi-channel data analysis. Gained broad international acceptance in both government and private sector polygraph testing.
eupnea Physiology
Eupnea is normal, quiet breathing at rest. In polygraph testing, eupnea represents the baseline respiratory pattern against which changes during the test — such as suppression, Apnea, or acceleration — are compared.
event marker Scoring
Event markers are annotations placed on the polygraph chart to alert reviewers of significant events: question onset and offset, the examinee's answer, movements, talking, deep breaths, and other occurrences. Many event markers have universally accepted meanings within the polygraph profession.
Event-Specific Testing Techniques
A polygraph examination format focused on a single specific event or incident (e.g., a particular theft, assault, or security breach). Considered the most accurate form of diagnostic polygraph testing because the examinee's attention is concentrated on one clearly defined issue. APA standards strongly recommend event-specific formats for investigative and evidentiary applications. See also Single-Issue Test.
Evidence Connecting Question Techniques
A type of relevant question in the Federal ZCT format that asks about a connection to evidence related to the crime rather than the crime itself (e.g., "Were your fingerprints on the safe?"). Used alongside primary involvement and secondary involvement relevant questions to cover multiple aspects of an investigation in a single polygraph examination.
evidentiary decision rules Scoring
Evidentiary decision rules are a set of decision criteria proposed by Krapohl (2005) for 7-position scoring. They use asymmetric cutting scores: a grand sum of -6 or lower yields DI; +4 or greater yields NDI. When grand sums fall between -5 and +3, spot scores are evaluated — if any relevant ques...
evidentiary examination Practice
An evidentiary examination is a polygraph test where all parties agree in advance that the purpose is to provide a diagnostic opinion as evidence in a pending judicial proceeding. This represents the highest-stakes application of PDD and typically requires the most rigorous adherence to Standards...
A polygraph examination conducted under agreement (stipulation) between parties in a legal proceeding, where the results may be admitted as evidence in court. Requires strict adherence to APA standards, validated techniques, and quality control review. Evidentiary tests must use single-issue diagnostic formats with approved scoring methods. Admissibility varies by jurisdiction.
evoked cortical potentials Physiology
Evoked cortical potentials are brain waves induced by stimuli controlled by the experimenter. They are the broader category of which event-related potentials are a specific type. Research into evoked potentials for deception detection examines whether brain responses to crime-relevant stimuli dif...
ex parte phenomenon Legal
The ex parte phenomenon (Latin: \"taken from one side\") is a legal term applied in polygraph contexts to describe the \"friendly polygrapher\" hypothesis — the notion that an examiner hired by the examinee's attorney may produce less accurate results because the examinee has reduced fear of adverse ...
Examination Report Practice
The formal written document produced by the examiner after a polygraph examination. Includes examinee identification, date and location, purpose, testing technique used, all questions asked, number of charts collected, scoring method and results, any admissions, the diagnostic or screening opinion, and the examiner's credentials. APA standards require specific elements in all reports.
Examinee Practice
The person undergoing a polygraph examination. The examinee's rights include informed consent, the right to stop the test at any time, the right to review all test questions beforehand, and confidentiality of results. Examiners must verify suitability before proceeding. See how a polygraph test works for a full walkthrough.
Examiner Bias Practice
The potential for an examiner's prior knowledge of case facts, victim statements, or investigative suspicions to unconsciously influence test administration or scoring. Blind review and automated scoring algorithms are designed to mitigate examiner bias. APA standards recommend that examiners avoid excessive case detail knowledge that could compromise objectivity.
exculpatory examination Practice
An exculpatory examination is a PDD test offered to an accused person against whom other strong evidence already exists. Common in military settings where urinalysis has indicated illegal drug use, the exculpatory exam gives the accused an opportunity to present evidence supporting innocence. The...
exosomatic Physiology
Exosomatic refers to measurements using externally applied electrical current. In electrodermal recording, exosomatic methods apply current to the skin to measure either conductance (constant voltage) or resistance (constant current). Both skin conductance and skin resistance are exosomatic measu...
experimental group Practice
The experimental group receives the treatment or manipulation of interest in a research study. In PDD research, the guilty/deceptive group is typically the experimental group (they commit a mock crime), while the innocent group serves as the control. Comparing the physiological responses between ...
exploratory test Techniques
The exploratory test is a Zone Comparison Technique format designed for addressing multiple issues within a single test. It allows examiners to explore several relevant topics to identify which ones produce significant physiological responses, potentially guiding subsequent single-issue testing.
extrapolygraphic Practice
Extrapolygraphic describes information not derived exclusively from the polygraph waveforms. Sources include case facts, behavioural indicators, and base rates. Some schools teach that extrapolygraphic information should inform the final decision (the clinical approach), while numerical analysis ...
extrasystolic beat Physiology
An extrasystolic beat is an older term for a premature ventricular contraction (PVC) — a heartbeat occurring outside the normal rhythm. In the cardiograph tracing, PVCs produce visible distortions that examiners must identify as artifacts rather than diagnostic responses. See: arrhythmia.
EyeDetect Instruments
An emerging credibility assessment technology that measures ocular changes (pupil dilation, eye movement, blink rate, fixation patterns) as indicators of cognitive load associated with deception. Not a traditional polygraph instrument and not currently APA-validated. Used as a supplementary or preliminary screening tool in some settings.
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false key Practice
A false key is a deliberately placed distracter item in a Known-Solution Peak of Tension test. The examiner hints it is the correct item, but it is by design incorrect. Its purpose is to divert the attention of innocent examinees who do not know the true critical item. The false key is the most p...
False Negative Results
An erroneous polygraph result where a deceptive examinee is incorrectly classified as truthful (NDI). Minimising false negatives is critical in security screening and criminal investigation. APA-validated techniques and algorithms are designed to balance false negative and false positive rates.
False Positive Results
An erroneous polygraph result where a truthful examinee is incorrectly classified as deceptive (DI). False positives can have serious personal and professional consequences. Proper examiner technique, validated scoring methods, and quality control review help minimise false positive rates in polygraph testing.
fear of detection model Theory
The fear of detection model proposes that deceptive examinees respond physiologically to relevant questions from fear that their deception will be uncovered and adverse consequences will follow. The greater the fear, the greater the response.
fear of error Theory
Fear of error is a concept by James Matte proposing that innocent examinees may react to relevant questions due to excessive concern about a false positive error. To address this, Matte developed \"inside track\" questions for his Quadri-Track Zone Comparison Technique. Independent empirical suppor...
Feature Extraction Scoring
The process of identifying and measuring specific physiological response characteristics from raw polygraph data for use in scoring algorithms. Features include EDA amplitude, respiratory line length, cardiovascular baseline rise, and pulse amplitude changes. Automated feature extraction by computer algorithms reduces subjectivity and improves consistency compared to visual inspection by human scorers.
Polygraph testing conducted by U.S. federal agencies including the FBI, CIA, NSA, DIA, DEA, Secret Service, and Department of Energy for purposes of pre-employment screening, security clearance vetting, counterintelligence, and criminal investigation. Federal programs operate under standardised guidelines and require examiners to be trained at the NCCA or an equivalent federally approved program.
field research Practice
Field research in PDD uses actual polygraph cases conducted by practising examiners on real suspects, witnesses, and victims. This contrasts with laboratory research using mock-crime scenarios. Field studies offer ecological validity but face challenges in establishing Ground Truth.
Field Study Results
Polygraph research conducted using real-world examination data from confirmed cases, as opposed to laboratory mock-crime studies. Field studies provide ecologically valid accuracy estimates because they reflect genuine stakes, real emotional arousal, and actual examiner–examinee dynamics. The National Academy of Sciences (2003) emphasised the importance of field studies for establishing polygraph validity.
Fight-or-Flight Response Physiology
The body's acute stress response mediated by the sympathetic branch of the autonomic nervous system. Triggers physiological changes including increased heart rate, elevated blood pressure, and increased sweat gland activity — all of which are recorded by the polygraph. Deception can activate this response as the brain perceives the threat of being caught in a lie.
fight, flight, freeze Theory
Fight, flight, freeze (F3) are three stereotypical behavioural responses to threat. The physiological responses — mobilising energy, narrowing attention — are the same across all three and are recorded during PDD testing. Handler & Honts (2007; 2008) offered an alternative explanation based on th...
finger of death Physiology
The finger of death is an informal term for a tracing pattern in the electrodermal channel — a sudden plunge after a Relevant Question followed by a normal return to baseline. Some attribute it to sensor contact loss during physical countermeasures. The phenomenon is not well understood and is no...
Metal or Ag/AgCl electrodes attached to two fingers of the examinee's hand to measure electrodermal activity (EDA) during a polygraph examination. A small, imperceptible electrical current passes between the plates, and changes in skin conductance caused by sweat gland activity are recorded as the EDA channel. Proper electrode placement and contact gel application are essential for data quality.
Fleiss' kappa Scoring
Fleiss' kappa is a statistical measure of agreement among multiple raters classifying items into categories. In PDD, it provides a metric for Interrater Reliability — how consistently different examiners reach the same conclusions from the same polygraph charts. It is the preferred method for gau...
A neuroimaging technology that detects changes in blood oxygenation in the brain as a proxy for neural activity. Investigated as a potential deception detection method based on the premise that lying activates specific brain regions (prefrontal cortex, anterior cingulate). Not a polygraph instrument. Currently limited to research settings due to cost, immobility, and insufficient validation for individual-level diagnostic use.
foil Practice
A foil is an irrelevant item in a Concealed Information Test. Foils are designed to appear equally plausible to innocent examinees as the critical item. Also called padding, buffer, control, or non-critical item.
The forensic psychophysiological detection of deception examination encompasses all activities between a forensic psychophysiologist and an examinee: the Pre-Test Interview, physiological data collection during testing, data analysis to support a diagnostic decision, and the post-test phase. See:...
forensic psychophysiologist Practice
A forensic psychophysiologist is a proposed alternate title for a polygraph examiner — a person who has completed an APA-accredited academic programme in forensic psychophysiology, including an appropriate internship.
forensic psychophysiology Practice
Forensic psychophysiology was defined by Dr. William J. Yankee (1992) as the science dealing with the relationship and applications of PDD tests to the legal system. The \"forensic\" modifier distinguishes this discipline from the broader field of psychophysiology.
format Practice
A format in polygraph testing refers to the particular order of question presentations, the rules governing that order, and the types of questions used. \"Format\" is sometimes incorrectly used interchangeably with \"technique,\" which is a broader term encompassing not only the format but all practi...
frame of reference Practice
The frame of reference consists of the circumstances or facts — crime report, criminal complaint, victim allegation — presented to the polygraph examiner that form the basis for the PDD examination. A clear and accurate frame of reference is essential for formulating effective test questions.
The friendly polygrapher hypothesis, proposed by Martin Orne, suggests that a deceptive examinee would be harder to detect when tested by an examiner hired by the examinee's own attorney, because fear of consequences is reduced. All field studies investigating this hypothesis have failed to find ...
The original legal standard for admissibility of scientific evidence in U.S. courts, established when polygraph evidence was first presented (and rejected) in court. Required that scientific techniques be "generally accepted" in the relevant scientific community. Largely superseded by the Daubert standard in federal courts (1993), though some states still apply the Frye test. The Frye case established the first precedent for exclusion of lie detector results.
The most comprehensive security screening polygraph examination. Covers counterintelligence issues (espionage, sabotage) plus personal conduct areas including drug use, criminal activity, financial issues, and foreign contacts. Required for CIA, NSA, and certain DIA positions. More extensive than the Counterintelligence Scope Polygraph (CSP).
Functional Near-Infrared Spectroscopy Techniques
Functional near-infrared spectroscopy (fNIRS) is a neuroimaging technique using infrared laser light to measure brain activity. Light absorption/reflection patterns indicate where oxygenated blood concentrates, inferring active brain regions. fNIRS has been experimentally tried for deception dete...
The standard polygraph format used by most U.S. federal agencies. A variant of the Backster Zone Comparison Test adapted for government use. May address multiple aspects of an investigation in a single chart, including primary involvement, secondary involvement, and evidence connecting questions. Scored using seven-position TDA or ESS methods. The most widely administered diagnostic format in federal polygraph programs.
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galvanograph Instruments
The galvanograph is the polygraph component responsible for producing the graphic recording of skin resistance. The term dates from the era of analog polygraphs and reflects the historical use of galvanic skin response (GSR) measurement.
ganglion Physiology
A ganglion (plural: ganglia) is a cluster of nerve cell bodies located outside the central nervous system. Ganglia serve as relay stations in the Autonomic Nervous System, including the sympathetic chain ganglia that are important to PDD because they mediate the sympathetic responses the polygrap...
general nervous tension Physiology
General nervous tension (GNT) describes physiological patterns suggesting the examinee's basal Arousal level is elevated — fast heart rate, labile electrodermal activity, and uneven breathing. GNT is not indicative of deception in itself. Examiners attempt to bring the examinee to a moderate arou...
general question technique Techniques
The general question technique is an alternate expression for the Keeler Relevant/Irrelevant Technique, one of the earliest structured polygraph testing methods.
generalizability Practice
Generalizability is the extent to which research results can be translated to other settings or to real-world applications. In PDD, it addresses whether findings from laboratory mock-crime studies apply to actual criminal investigations, and whether results from one population generalise to others.
The original name for the Concealed Information Test (CIT), developed by David Lykken in the 1950s. Tests whether an examinee recognises crime-relevant details by presenting multiple-choice items and monitoring for differential physiological responses to the critical item. Widely used in Japan's criminal justice system and extensively validated in laboratory research. See also Concealed Information Test.
global analysis Practice
Global analysis evaluates polygraph recordings as a whole and may include extrapolygraphic information such as examinee behaviour and case facts. Championed by Reid and Arther, it contrasts with the purely numerical approach. Also called the clinical approach.
A subjective method of polygraph chart analysis where the examiner evaluates the overall pattern of physiological responses across all charts and channels without assigning numerical scores to individual questions. Considered less reliable and reproducible than numerical scoring methods. Largely replaced by structured scoring systems in modern practice.
Grand Total Rule Scoring
A decision rule used in the Empirical Scoring System (ESS) where the sum of all comparison-to-relevant scores across all charts determines the final test outcome. If the grand total exceeds the positive cut-score, NDI is indicated; if below the negative cut-score, DI is indicated; values between the cut-scores yield an Inconclusive result.
Green Zone Techniques
In Backster's Zone Comparison Test, the portion of the question sequence containing probable-lie comparison questions. Truthful examinees are expected to show their strongest physiological responses in the Green Zone (to comparison questions), while deceptive examinees respond more strongly in the Red Zone (to relevant questions). See also Red Zone and Black Zone.
Ground Truth Scoring
The independently verified actual truth or deception status of an examinee, established through confessions, DNA evidence, physical evidence, or other conclusive means external to the polygraph. Ground truth is essential for validating polygraph techniques because it provides the criterion against which accuracy, sensitivity, and specificity are calculated. Also referred to as the criterion variable.
GSG Physiology
GSG is a non-standard expression created by a polygraph manufacturer to represent skin conductance measurement. It adapted \"GSR\" (Galvanic Skin Response) by replacing \"R\" with \"G\" (the engineering shorthand for conductance). Since GSR stands for Galvanic Skin Response (not Resistance), the substi...
An older term for electrodermal activity (EDA). Refers to changes in the electrical resistance of the skin caused by sweat gland activity. Now largely replaced in professional terminology by EDA or EDR, though GSR remains commonly used in non-technical contexts and consumer-facing descriptions of lie detector tests.
Guilt Complex Question Techniques
A question type originally introduced by John Reid designed as a known-truth answer to what appears to be a relevant question about a crime the examinee is known not to have committed. Used to identify examinees who respond strongly to any accusatory question regardless of guilt — potentially indicating extreme anxiety or a "guilt complex" personality rather than actual deception.
guilt complex reactor Practice
A guilt complex reactor is a hypothetical personality type that causes innocent examinees to respond physiologically to any question they consider accusatory. Guilt complex questions have been used in various polygraph formats to identify such examinees. However, no empirical evidence supports ei...
guilt complex test Techniques
The guilt complex test is a PDD format in which the examinee is tested on a fabricated crime to determine whether they react to accusatory questions regardless of actual involvement. Its hypothetical purpose was avoiding false positive outcomes. It was taught in early Reid and Keeler schools but ...
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Habituation Physiology
The progressive decrease in physiological response magnitude when a stimulus is repeated without consequence. In polygraph testing, habituation explains why responses to irrelevant and neutral questions tend to diminish over successive chart presentations. Habituation must be distinguished from fatigue and deliberate suppression. Stimulus novelty in CIT/GKT protocols is designed to minimise habituation effects.
halo effect Practice
The halo effect is the tendency of an observer to be unduly influenced by a single trait of an individual. For PDD examiners, it represents a potential source of error if interpersonal impressions of the examinee influence the diagnostic decision. This is one reason modern practice emphasises Num...
heart rate Physiology
Heart rate is the rate of ventricular contractions, measured in beats per minute. It is one index of physiological Arousal. Research indicates that after stimulus onset, cardiac arousal initially takes the form of a heart rate decrease if the response is an orienting response. Heart rate and the ...
hertz Instruments
Hertz (Hz) is the unit of frequency measured in cycles per second. Named for German physicist Heinrich Hertz, it is used in PDD to describe engineering specifications of polygraph instruments and the frequency bands analysed in voice stress technologies (e.g., the 8–10 Hz microtremor range).
Hg Instruments
Hg is the chemical symbol for mercury (from Latin hydrargyrum). In polygraph notation, blood pressure cuff pressure is expressed in millimetres of mercury (e.g., 72 mm Hg). It is the standard unit of measure for the sphygmomanometer used in cardiovascular recording.
Hit Rate Scoring
The overall percentage of correct classifications (both true positives and true negatives) produced by a polygraph technique or scoring method. Hit rate combines sensitivity and specificity into a single measure of overall accuracy. While intuitive, hit rate can be misleading in populations with unequal base rates of deception and should be interpreted alongside sensitivity and specificity separately.
Hobson's Choice Theory
Hobson's Choice — named for a stable owner who offered customers the nearest horse or none — describes an apparent choice with no genuine alternative. In polygraph methodology, it describes the dynamic during probable-lie comparison question development: the examinee feels compelled to deny a beh...
homeostasis Physiology
Homeostasis describes the maintenance of internal physiological stability within a prescribed range. While organisms are always in a state of homeostasis (except during illness), the modern concept of allostasis has largely replaced homeostasis as the central framework for understanding physiolog...
hope of error Theory
Hope of error is a concept by James Matte proposing that deceptive examinees hope the polygraph will produce a false negative error. It is a central component of his Quadri-Track Zone Comparison Technique, where a direct question about this hope is scored as a Relevant Question. Critics note that...
Horizontal Scoring System Scoring
The Horizontal Scoring System is a rank-order scoring method by Gordon and Cochetti (1980s). All responses within each channel are ranked by magnitude; ranks for comparison questions receive positive values, relevant questions negative values. The method is used with the IZCT but may be limited t...
Hybrid Test Techniques
A polygraph examination that combines elements from different testing formats, such as using directed-lie comparison questions within a Zone Comparison Test structure. Hybrid approaches may be used when standard single-format techniques are insufficient for the complexity of the case.
hydrosphygmograph Instruments
The hydrosphygmograph was a device used by Cesare Lombroso in the late 19th century to detect blood pressure changes during interrogation. An examinee's fist was placed in a sealed water container, and volume changes were recorded on a smoked drum. It is the first mechanical device reported in th...
Hyperreactivity Results
An examinee condition where physiological responses are excessively strong across all question types (relevant, comparison, and irrelevant), making it difficult to differentiate meaningful reactions from general arousal. Can be caused by extreme anxiety, medical conditions, stimulant medications, or caffeine.
hyperventilation Physiology
Hyperventilation is an increase in the rate and depth of breathing beyond metabolic needs. In polygraph testing, hyperventilation appearing in the respiratory tracings may indicate anxiety, a medical condition, or an attempt at countermeasure activity.
hypnosis Practice
Hypnosis is an altered state of consciousness with heightened receptivity to suggestion. It has been discussed as a potential undetectable countermeasure — theoretically allowing memories to be blocked or altered, undermining physiological responsiveness. The limited available research has not co...
Hyporeactivity Results
An examinee condition where physiological responses are abnormally weak or flat across all channels and question types. Can be caused by sedatives, beta-blockers, extreme fatigue, certain medical conditions, or deliberate suppression attempts. May render the examination unsuitable for scoring.
hypothenar eminence Physiology
The hypothenar eminence is the fleshy prominence on the palm at the base of the little finger. Along with the thenar eminence, it is one of the most productive recording sites for electrodermal activity due to its high concentration of eccrine sweat glands.
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imagery Practice
Imagery — the use of visualisation to experience memories or fantasies — can produce profound physiological responses and is a concern as a covert mental countermeasure. Because it is performed entirely internally, it is difficult for examiners to detect. Imagery is one form of dissociation.
impedance cardiogram Instruments
An impedance cardiogram (ICG) is a specialised cardiovascular recording from which heart timing and stroke volume can be derived. While not currently standard in PDD, research shows it can gauge sympathetic arousal when used with an ECG, as the pre-ejection period (PEP) derived from these combine...
A prominent legal scholar and polygraph pioneer at Northwestern University who co-authored Criminal Interrogation and Confessions with John Reid. A student of Leonarde Keeler, Inbau contributed significantly to the legal framework surrounding polygraph evidence and interview techniques. His work laid the foundation for both polygraph testing methodology and interrogation science in the United States.
A polygraph result where physiological data does not clearly indicate either deception or truthfulness. The examinee cannot be classified as DI or NDI based on the available data. APA standards require the result be reported as inconclusive (not forced into a definitive call). Retesting may be recommended. Typical inconclusive rates range from 5–15% of examinations.
Incomplete Practice
Incomplete is a PDD outcome indicating testing was terminated before sufficient physiological data were collected — due to health problems, emotional distress, equipment issues, or the examinee's unwillingness to continue. An incomplete implies testing may continue at a future date, unlike an inc...
Inconclusive Rate Results
The percentage of polygraph examinations that produce an inconclusive (INC) result, meaning the data does not clearly indicate either deception or truthfulness. Typical inconclusive rates for validated techniques range from 5–15%. Lower cut-scores reduce inconclusives but may increase false positive rates; higher cut-scores increase inconclusives but improve specificity. The inconclusive rate is a key parameter in evaluating scoring system performance.
indefinite Practice
Indefinite is an alternate term for Inconclusive — a PDD outcome where testing was completed but neither deception nor truthfulness could be diagnosed.
independent variable Scoring
The independent variable is manipulated by the experimenter to observe its effects on the dependent variable. In PDD research studying sex differences in accuracy, the independent variable would be the examinee's gender and the dependent variable would be the technique's accuracy for each group.
information gain Scoring
Information gain is a statistical measure of how much a technique improves decision-making over not using the technique. In forensic applications, the polygraph has been shown to provide significant information gain over unassisted judgments across a wide range of base rates. In screening, only d...
Informed Consent Practice
A mandatory pre-test requirement where the examinee acknowledges in writing that they understand the polygraph process, their rights (including the right to stop at any time), how results will be used and disclosed, and that they are participating voluntarily. Examination without informed consent is a violation of APA standards and may constitute legal liability.
innervation Practice
Innervation means to provide nerve supply or to stimulate an organ through its nerves. The concept is fundamental to understanding how the Autonomic Nervous System controls the organs and glands that produce the physiological responses measured by the polygraph.
inside track Techniques
The inside track is one of three tracks in the Quadri-Track Zone Comparison Technique. It contains two questions: one addressing the examinee's fear of false positive error (used as a comparison question) and another addressing the hope of false negative error (treated as a relevant question). In...
inspiration/expiration ratio Techniques
The inspiration/expiration (I/E) ratio compares inhalation duration to exhalation duration. Normally about 1:2 at rest, it was first reported by Benussi (1914) to change during deception. However, more recent research has not found it to be of strong diagnostic value in manual scoring, and Benuss...
instant offense examination Techniques
An instant offense examination is a form of PCSOT conducted when a subject denies the offense or a significant element of it. It is used to break through denial barriers and may also be given when new allegations arise during probation or parole. Also called a specific issue examination.
integument Physiology
The integument is the body's covering — the skin. Consisting of epidermis, dermis, and subdermis, the skin houses the eccrine sweat glands that produce the electrodermal activity measured by the polygraph. It also contains sensory receptors for touch, pain, and temperature.
intent question Practice
An intent question asks whether the examinee engaged in an act with criminal intent rather than merely whether they committed the act. It is considered the least reliable type of Relevant Question and is avoided when possible. Some behavioural acts (e.g., \"sexual contact\") include intent by defin...
inter-chart stimulation Techniques
Inter-chart stimulation is the examiner-examinee interaction occurring between individual test charts. It may include reminders to answer truthfully or further emphasis of comparison questions. Research suggests it may improve validity but it remains controversial.
interbeat interval Physiology
The interbeat interval (IBI) is the period between cardiac pulse waves, measured systole to systole. IBI shortens after stress onset (defence response) and lengthens during orienting responses. IBI and heart rate are reciprocals of each other.
Interrater Reliability Scoring
A measure of consistency between different examiners scoring the same polygraph charts. High interrater reliability indicates that the scoring system produces consistent results regardless of who performs the analysis. Research shows that structured scoring systems (ESS, 7-position) and automated algorithms (OSS-3) produce significantly higher interrater reliability than global evaluation methods.
Interrogation Practice
A formal process of questioning a suspect, distinct from the polygraph examination itself. While some historical polygraph practices blended interrogation with testing, modern APA standards clearly separate the polygraph examination (a scientific measurement process) from any subsequent interrogation or interview. Polygraph results may inform but should not replace proper investigative procedures.
investigative examination Practice
An investigative examination is a polygraph test intended to supplement an investigation, where the results are not expected to be tendered as court evidence. Types include applicant testing, counterintelligence screening, community safety examinations, and routine specific-issue diagnostic testing.
Irrelevant Question Techniques
A neutral question in a polygraph test designed to produce minimal physiological response (e.g., "Is today Tuesday?" or "Are you sitting down?"). Used to establish baseline physiological patterns, allow recovery between relevant questions, and re-establish the examinee's normal state between stimulus questions.
A polygraph technique developed by Nathan Gordon that integrates elements of the Zone Comparison Test with additional diagnostic features. APA-validated for event-specific (single-issue) diagnostic testing. Incorporates structured question sequences and behavioural analysis alongside physiological data.
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jackknife procedure Scoring
The jackknife procedure is a statistical technique for testing a model by systematically excluding one data set at a time and testing it against the model built from the remaining data. This produces a distribution of outcomes useful for validation. Jackknife procedures have been used in PDD algo...
A joint committee of the APA and the Association for the Treatment of Sexual Abusers (ATSA) that developed standardised guidelines for Post-Conviction Sex Offender Testing (PCSOT). JPCOT established the three standard PCSOT test types (Sexual History Disclosure, Monitoring, and Maintenance) and training requirements for examiners conducting sex offender polygraph testing.
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Karpman's classification of lying Practice
Karpman's classification of lying categorises lies by their underlying motives: benign (social convention), hysterical (attention-seeking), defensive (avoiding adverse situations), compensatory (impressing others), malicious (personal gain), gossip (exaggeration), implied (partial truths), \"love ...
Keeler Polygraph Instruments
An early three-channel polygraph instrument developed by Leonarde Keeler in the 1930s at Northwestern University. Combined cardiovascular, respiratory, and galvanic skin response measurements into a single portable device. The Keeler Polygraph was the first commercially produced polygraph instrument and became the standard for law enforcement use for several decades. Now of historical significance only.
Keeler Technique Techniques
The Keeler Technique is a Relevant/Irrelevant testing method devised by Leonarde Keeler for single- and multiple-issue testing. Once dominant in the field, its popularity has declined since the introduction of CQT formats. Among screening techniques that have undergone validity research, the R/I ...
A pioneering figure in polygraph history who refined the modern polygraph instrument at Northwestern University in the 1920s–1930s. Keeler added the galvanic skin response channel to the existing cardiovascular and respiratory components, creating the multi-channel instrument recognisable today. Founded the Keeler Polygraph Institute in Chicago. John Reid and Fred Inbau were among his students.
key Practice
The key is the critical item in a Peak of Tension Test. In a known-solution POT, it contains incriminating information only the guilty person should know. In a searching POT, it holds information the examiner is trying to uncover. In stimulation tests, it is the item the examinee is directed to l...
key word method Techniques
The key word method requires examinees to repeat an important word from each test question along with their yes/no answer. Based on stimulus–stimulus theory, it ensures cognitive engagement with the question content and is used to neutralise dissociation countermeasures.
Kircher Features Scoring
A set of physiological response features first described by researchers at the University of Utah in the 1980s. Include the amplitude of increase for electrodermal and cardiovascular activity, and reduction of respiratory activity. Kircher features form the basis for most modern polygraph scoring algorithms including OSS-3, PolyScore, and ESS. Can be extracted both visually and by automated computer methods.
A Peak of Tension Test variant where the examiner knows which item in the sequence is crime-relevant and monitors for a peak physiological response at that item. Used to assess examinee knowledge of specific crime details (e.g., the exact amount stolen, the weapon used, the location of evidence). See also Peak of Tension Test.
kymographion Instruments
A kymographion is a mechanical device using clockwork to rotate a drum covered in smoked paper, on which a stylus scratches tracings of physiological or other phenomena. It was the forerunner of what would later become the kymograph used in polygraph instruments.
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labile Practice
Labile means unstable, inconsistent, or dynamic. In PDD, tracings displaying a high degree of responsivity or broad amplitude changes are described as labile. A highly labile electrodermal tracing, for example, shows frequent spontaneous responses. The opposite is stabile.
laboratory research Practice
Laboratory research uses experimental procedures designed to mimic real-world circumstances under controlled conditions, such as mock-crime studies. While laboratory studies offer control over variables and clear Ground Truth, they have been criticised for not inducing the same emotional involvem...
Polygraph research conducted in a controlled laboratory setting where participants are instructed to commit a simulated crime and then tested. While laboratory studies allow precise control of variables and confirmed ground truth, they may underestimate real-world accuracy because participants face no genuine consequences for deception. Often contrasted with field studies for ecological validity.
Lafayette Instrument Company Instruments
A major manufacturer of computerised polygraph instruments widely used by U.S. federal agencies (including DIA and other DoD entities), law enforcement, and private examiners. Lafayette systems integrate the LXSoftware platform with PolyScore and other scoring algorithms for digital data acquisition and analysis.
A medical student and police officer in Berkeley, California, who in 1921 developed the first continuous multi-channel polygraph instrument for use in criminal investigation. Larson's device simultaneously recorded blood pressure, pulse, and respiration during questioning — establishing the fundamental design principle of the modern polygraph. His work at the Berkeley Police Department under Chief August Vollmer marked the beginning of scientific lie detection in law enforcement.
latency Practice
Latency is the delay between stimulus presentation and some aspect of the physiological response. Electrodermal onset latency is typically 1–3 seconds; hormonal blood pressure effects take longer. Departures from typical latencies may indicate the response is unrelated to the stimulus, attentiona...
law of initial values Theory
The law of initial values (LIV) states that a physiological response's magnitude is constrained by the current arousal level. If Arousal is already high, the response from that elevated baseline will be smaller than if the same stimulus occurred at a moderate level. This ceiling effect is relevan...
law of intensity Theory
The law of intensity states that within limits, response magnitudes and stimulus intensities share a log-linear relationship — stronger stimuli produce larger responses. In PDD, response magnitudes are used to infer which question type the examinee considers most psychologically salient or threat...
Layered Voice Analysis Instruments
Layered Voice Analysis (LVA) is a voice-based technology marketed for detecting emotions and deception. Developed by Nemesysco, Ltd. (Israel), it applies algorithms to the voice signal. Independent research has consistently found its validity for deception detection to be poor to non-existent. Th...
lens model Theory
The lens model (Brunswik, 1950s) studies decision rules used by human decision-makers by characterising how they select and weigh cues to assess reality. Applied to PDD at the University of Utah, it helps evaluate which physiological features examiners use, how they weigh them, and what combinati...
A polygraph screening format designed specifically for pre-employment vetting of law enforcement candidates. Addresses topics such as criminal history, drug use, integrity, and truthfulness on the application. Structurally similar to the Utah MGQT and other validated screening formats. Widely used by police departments and sheriff's offices.
The legal requirement in 21 U.S. states for polygraph examiners to obtain a state-issued licence before conducting examinations. Licensing requirements vary by state but typically include completion of APA-accredited training, supervised field experience, passing a state examination, and maintaining continuing education. Practising without a licence where required is a criminal offence.
lie detector Practice
Lie detector is a common but inaccurate term for the polygraph. The instrument does not detect lies directly — it records physiological changes associated with deception. Professional examiners and the APA prefer \"polygraph\" or \"polygraph examination.\" The scientific term is psychophysiological d...
likelihood ratio Scoring
The likelihood ratio (LR) indicates how much a polygraph result changes the probability of deception compared to pre-test probability. LR+ tells how much more likely deception is after failing; LR- tells how much more likely truthfulness is after passing. LRs include inconclusive results and gene...
Limestone Technologies Instruments
A Canadian manufacturer of computerised polygraph instruments. Their systems incorporate the Empirical Scoring System (ESS-M) algorithm and are used internationally in both government and private sector polygraph testing. Known for the Paragon and Converus platforms.
Logistic Regression Scoring
A statistical classification method used in polygraph scoring algorithms (including OSS-3) that estimates the probability of deception based on weighted combinations of physiological response features. Logistic regression models output a probability value between 0 and 1, which is compared against empirically derived cut-scores to classify the examinee as deceptive, truthful, or inconclusive.
Lognormal Ratio Scoring
A mathematical transformation applied to physiological response measurements in the OSS-3 algorithm. Converts raw comparison-to-relevant response ratios into lognormal distributions for more reliable statistical analysis. Reduces the impact of outliers and normalises score distributions, enabling the use of parametric decision models for classification.
Lombroso, Cesare Practice
Cesare Lombroso (1835–1909) was an Italian physician who first employed instrumentation to detect deception in live criminal investigations. He reported in 1885 using a hydrosphygmograph to detect blood pressure changes during interrogation — the first mechanical device used specifically for dece...
Luria, Aleksandr Practice
Aleksandr Luria (1902–1977) was a Russian researcher who originated conflict theory — one of the theoretical explanations for PDD mechanisms. Luria conducted deception experiments using a tremograph and proposed that incompatible emotions affect bodily responses in measurable ways.
LXSoftware Instruments
The proprietary software platform used with Lafayette Instrument Company polygraph systems for data acquisition, display, and analysis. Integrates real-time physiological monitoring with automated scoring algorithms including PolyScore. Used by many U.S. federal agencies and law enforcement departments. Supports electronic data storage, report generation, and quality control review.
Lykken scoring Scoring
Lykken scoring is a system for scoring electrodermal responses in the Concealed Information Test. It compares critical item responses against neutral items using a rank-order method. One variant uses averaged ranks. It established the threshold framework for CIT decision-making.
Lykken, David T. Practice
David T. Lykken (1928–2006) was a psychologist and prominent critic of the CQT. His book A Tremor in the Blood argued the CQT was fatally flawed. Lykken advocated the Guilty Knowledge Test (now Concealed Information Test) as an alternative. While he did not publish original CQT research, his crit...
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Maintenance Test Techniques
A recurring polygraph examination administered periodically (typically every 6–12 months) to convicted sex offenders or other supervised individuals to verify ongoing compliance with treatment or supervision conditions. One of the three standard PCSOT sub-types. Addresses current behaviour since the last examination rather than historical conduct.
manual mode Techniques
Manual mode is a setting on the electrodermal activity channel where filtering of tonic activity is minimal, preserving the raw signal. All modern polygraphs include this option alongside automatic mode, allowing examiners to choose based on their training requirements.
Marey, Étienne-Jules Practice
Étienne-Jules Marey (1830–1904) was a French researcher and early physiologist who invented the sphygmograph — a device for recording blood pressure and pulse on a smoked drum. His portable physiological recorder was a precursor to instruments later incorporated into the polygraph.
A Zone Comparison Test variant developed by James Allan Matte that adds a fourth question track (fear-of-error questions) alongside relevant, comparison, and symptomatic questions. The fear-of-error component is designed to identify truthful examinees whose anxiety about the testing process itself may produce elevated responses to relevant questions. APA-validated technique.
mean blood pressure Physiology
Mean blood pressure is the average arterial pressure during the entire cardiac cycle. It can be approximated by averaging systolic and diastolic values, or by adding one-third of the pulse pressure to the diastolic value. In PDD, examiners assess relative blood pressure changes rather than absolu...
Medications & Polygraph Testing Practice
Certain medications can affect polygraph results by altering physiological responses. Beta-blockers may suppress cardiovascular responses; benzodiazepines and sedatives may reduce overall reactivity; stimulants may increase baseline arousal. Examiners must screen for medication use during suitability evaluation and note any medications in the examination report. Medications do not automatically disqualify an examinee but may affect data quality.
medulla oblongata Physiology
The medulla oblongata is a brain stem structure responsible for automatic control of respiratory and cardiovascular activity. It is directly associated with the physiological events that PDD data analysis evaluates — the involuntary changes in breathing and heart function that occur in response t...
Mental Countermeasure Practice
A cognitive technique used by an examinee to attempt to influence polygraph results, such as counting backwards by 7, performing mental arithmetic, visualising stressful imagery, or deliberately inducing emotional states during comparison questions. Research shows mental countermeasures can be difficult to detect instrumentally, making examiner vigilance and proper technique critical.
A systematic statistical review combining results from multiple polygraph validation studies to estimate overall accuracy rates and effect sizes. The APA meta-analytic survey (2011, updated by Nelson 2015) identifies 14 validated techniques with published accuracy data. Meta-analyses provide the strongest available evidence for technique validation and inform APA standards on approved testing methods.
A variation of the Comparison Question Test designed for multi-issue screening examinations. Commonly used in government security screening where multiple relevant topics (e.g., espionage, unauthorised disclosure, foreign contacts) must be addressed in a single polygraph examination session.
Microprocessor Instruments
The central computing component in modern digital polygraph instruments that converts analog physiological signals to digital data in real-time. Microprocessors enable high-resolution data sampling (typically 30–360 Hz per channel), automated artifact detection, real-time signal quality monitoring, and integration with computerised scoring algorithms.
microtremor Physiology
A microtremor is a low-frequency oscillation (8–12 Hz) in the human voice, claimed by voice stress device manufacturers to inversely correlate with stress. Independent research has not found any spectral component of the voice to be a reliable predictor of deception. Microtremors are the purporte...
The Minnesota Multiphasic Personality Inventory (MMPI) is a widely used personality assessment in psychology and psychiatry. In PDD literature, the psychopathy and social introversion-extroversion scales are frequently cited because they influence physiological arousal levels, particularly electr...
mixed issue test Techniques
A mixed issue test is any polygraph test in which there is little or no overlap among the relevant questions — each addresses a different topic. Also called a multiple-issue test, it is primarily used in screening applications.
Mixed Question Test Techniques
The Mixed Question Test is a Reid polygraph test variation in which the standard straight-through question order is changed and some questions are repeated. It is always conducted after the straight-through test and is one component of the Reid Technique.
model policy Practice
A model policy is a non-binding standard outlining best practices. The APA uses model policies to help agencies and clients understand good polygraph practices — covering police applicant screening, PCSOT, examinee suitability, and other areas — giving a competitive advantage to examiners who ado...
Modified Relevant Irrelevant technique Techniques
The Modified Relevant/Irrelevant (MRI) technique is a specific-issue PDD format based on the Keeler R/I but using situational comparison questions. Users discuss all issues during the Pre-Test Interview but may not review relevant questions word-for-word. Results incorporate extrapolygraphic info...
Monitoring Polygraph Techniques
A polygraph format used primarily with convicted sex offenders to verify compliance with the terms of probation or parole. Part of Post-Conviction Sex Offender Testing (PCSOT) programs. Addresses specific behavioural compliance rather than a single investigative issue.
Monte Carlo Analysis Scoring
A statistical technique used in polygraph research to estimate accuracy rates and confidence intervals by generating large numbers of simulated random samples from observed data. Used to validate scoring algorithms like OSS-3 and ESS, and to compare automated scoring accuracy against human examiners. Provides robust error estimates for polygraph decision rules.
Monte Carlo Method Scoring
A statistical technique using repeated random sampling to calculate normative parameters for polygraph scoring decisions. Used extensively in the development and validation of OSS-3 and ESS decision rules. Bootstrap Monte Carlo procedures generate confidence intervals for accuracy estimates and help determine optimal cut-scores from field examination data.
Mosso, Angelo Practice
Angelo Mosso (1846–1910) was a student of Cesare Lombroso who in 1896 developed the \"scientific cradle\" — a device recording bodily responses to fear by measuring balance changes caused by blood redistribution and breathing on a fulcrum-mounted platform.
motor nerves Physiology
Motor nerves (also called efferent nerves) carry impulses from the central nervous system to muscles and effector organs. They include the autonomic pathways that produce the involuntary physiological changes the polygraph records.
movement sensor Instruments
A movement sensor is a mechanical sensor that detects covert movements by the examinee. It is used to identify certain types of physical countermeasures — such as pressing toes against the floor or tensing muscles — that could affect the physiological recordings.
Multi-Facet Testing Techniques
A polygraph approach where a single examination addresses multiple distinct facets or aspects of the same general issue — for example, testing both whether the examinee committed an act and whether they planned or helped conceal it. Distinguished from multi-issue screening (which covers entirely separate topics). The Federal ZCT is structured as a multi-facet test.
A polygraph examination that addresses more than one specific target issue. Used in security screening, pre-employment, and compliance monitoring. Results are reported as SR (Significant Response) or NSR (No Significant Response) rather than DI/NDI. An examinee may be truthful on some relevant questions but deceptive on others.
multiple-facet test Techniques
A multiple-facet test is a format where relevant questions target different elements of the same crime (e.g., printing, passing, and possessing counterfeit currency). Spot scores rather than the overall score determine the deception diagnosis. The AFMGQT and Zone \"exploratory\" formats can be used...
Münsterberg, Hugo Practice
Hugo Münsterberg (1863–1916) was chairman of Harvard's Psychology Department who, in his 1908 book On the Witness Stand, proposed creating deception tests using cardiovascular, breathing, and electrodermal measures. He also described the Concealed Information Test concept. His student William Mar...
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A comprehensive review of polygraph science published by the U.S. National Research Council titled The Polygraph and Lie Detection. The NAS report acknowledged that polygraph testing can discriminate between deceptive and truthful individuals at rates above chance, but raised concerns about the theoretical basis, specificity in low base-rate screening populations, and the potential for countermeasures. The report has been both cited and critiqued by polygraph researchers.
The U.S. federal training center for government polygraph examiners, located at Fort Jackson, South Carolina. Formerly known as the Department of Defense Polygraph Institute (DoDPI) and the Defense Academy for Credibility Assessment (DACA). Trains examiners for all federal agencies and conducts polygraph research.
A diagnostic opinion indicating that physiological data from the polygraph examination shows no significant responses suggestive of deception to relevant test questions. The examinee's strongest responses were to comparison questions rather than relevant questions. NDI is used in single-issue diagnostic testing only.
A comparison question format used in the original Reid technique that does not exclude the time period or subject matter of the offence under investigation (e.g., "Have you ever stolen anything?" asked during a theft investigation). Backster argued that NECQs could be confused with relevant questions by deceptive examinees, increasing false negative rates. See also ECQ.
neuron Physiology
A neuron is the structural unit and conducting cell of the nervous system, consisting of a cell body (soma), dendrites, and axon. Neurons form the circuitry of the Autonomic Nervous System that processes stimuli and generates the physiological responses the polygraph records.
neurotransmitter Physiology
A neurotransmitter is a chemical that transmits signals between neurons or to effector organs. Key neurotransmitters in PDD include acetylcholine (controlling eccrine sweat glands) and norepinephrine (most sympathetic nerve endings). Pharmacological agents affecting neurotransmission are of inter...
Neutral Question Techniques
See Irrelevant Question. Questions designed to produce minimal response, used to establish or re-establish the examinee's baseline physiological state during a polygraph examination.
A test result where the collected polygraph data is not of sufficient quality to analyse or score. Distinct from Inconclusive (INC), which indicates analysable but ambiguous data. No Opinion results are typically caused by medical issues, medications, examiner error, excessive artifacts, or the examinee's inability to remain still or follow instructions.
No Opinion Results
No Opinion is an alternate term for an Inconclusive outcome, used primarily in the U.S. federal government. In some sectors it may denote an Incomplete result.
Nociceptive Response Physiology
A physiological reaction to pain stimuli that can produce artifacts in polygraph data. Physical countermeasure techniques such as tongue biting, toe pressing, or pricking the skin with a concealed object rely on nociceptive responses to artificially generate physiological arousal during comparison questions. Activity sensors and examiner observation are used to detect these attempts.
non-specific responses Physiology
Non-specific responses are physiological responses that do not appear related to any identifiable external stimulus. A high incidence of spontaneous, non-specific responses can indicate elevated general Arousal and may complicate chart interpretation.
noradrenaline Physiology
Noradrenaline is the British term for norepinephrine — the primary neurotransmitter released by most adrenergic (sympathetic) nerve endings. It plays a central role in the sympathetic nervous system responses measured by the polygraph.
norm Practice
Norm is shorthand currently used by some PDD examiners for an Irrelevant Question in Relevant/Irrelevant and CQT formats. Also called neutrals.
An APA-accredited polygraph training school offering basic examiner courses, advanced training, and continuing education programs. One of several approved schools that provide the required 400+ hours of instruction for prospective polygraph examiners seeking APA membership and professional certification.
Used in multi-issue screening tests (not diagnostic single-issue tests). Indicates no significant physiological responses to any of the relevant questions, generally suggesting truthfulness across all tested issues. The screening equivalent of NDI in diagnostic testing.
numerical chart analysis Scoring
Numerical chart analysis renders polygraph decisions based exclusively on numeric values assigned to physiological responses. It does not consider extrapolygraphic information. Its four components are: feature identification, numerical value assignment, computation, and decision rules. Methods in...
Numerical Scoring Scoring
A structured method of evaluating polygraph charts by assigning numerical values to physiological responses at each relevant question. Scores are assigned using a 3-position (+1, 0, −1) or 7-position (+3 to −3) scale based on the magnitude of response difference between relevant and comparison questions. More reliable and reproducible than global evaluation.
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Oculomotor Deception Test Techniques
The Oculomotor Deception Test is an experimental Credibility Assessment technology using eye movements, pupillary responses, and reaction times as examinees read statements and press keys for true/false. It is based on the principle that deceptive responses require additional cognitive processing...
operant conditioning Techniques
Operant conditioning provides reward or punishment depending on preceding behaviour. Biofeedback uses operant conditioning to help people regulate autonomic responses, making it a theoretical method for teaching polygraph countermeasures. However, the limited research evaluating biofeedback train...
An involuntary physiological reaction to a novel or significant stimulus, characterised by increased skin conductance, heart rate deceleration, and changes in respiration. In polygraph testing, the orienting response is central to the Concealed Information Test (CIT) — guilty examinees produce stronger orienting responses to crime-relevant stimuli they recognise. First described by Pavlov and extensively studied by Sokolov.
One of the most widely validated computerised polygraph scoring algorithms, developed by Nelson, Krapohl, and Handler. Uses a logistic regression formula trained on confirmed field polygraph cases. Inputs include Kircher features from respiratory, electrodermal, and cardiovascular channels. Free and open-source. Research demonstrates accuracy exceeding 90% and performance superior to the average of human scorers.
Othello error Theory
The Othello error (coined by Paul Ekman) describes misattributing an innocent person's fear or distress as guilt. In PDD, this risk is mitigated by comparison questions that account for innocent examinees' general anxiety, reducing false positive errors from this source.
A psychological condition characterised by the delusional belief that a spouse or partner is being unfaithful, even without evidence. Relevant to polygraph practice because examinees with this condition may present atypical physiological responses during domestic issue (fidelity) testing. Examiners should be aware of this condition during suitability screening and pre-test interviews.
outlier Scoring
An outlier is a value far beyond the normal range. In PDD data, outliers may be excluded because they disproportionately influence statistical measures. What constitutes an outlier is typically established a priori. The concept became more prominent with computerised scoring algorithms and their ...
A concern, fear, or unresolved matter unrelated to the specific issue being tested that may affect the examinee's physiological responses during a polygraph examination. Outside issues can elevate baseline arousal and contaminate data. Symptomatic (outside-issue) questions in the ZCT are designed to detect these concerns. The pre-test interview also serves to identify and address outside issues before testing begins.
outside track Techniques
The outside track is one of the tracks in the Quadri-Track Zone Comparison Technique, consisting of two symptomatic questions. See: Matte (1996).
overall truth question Practice
An overall truth question addresses the examinee's general truthfulness or intention to be truthful during testing. It is used in some multiple-issue screening tests.
Overfitting Scoring
A statistical problem where a scoring algorithm performs very well on training data but poorly on new data. Occurs when too many features or variables are used to classify too few cases, creating an illusion of perfect accuracy. The National Academy of Sciences (2003) noted this risk in polygraph algorithm development. Proper cross-validation and independent replication studies are essential to avoid overfitting in polygraph scoring systems.
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P300 Techniques
The P300 is a brain wave (event-related potential) occurring ~300 ms after stimulus onset, associated with cognitive recognition of meaningful or rare stimuli. A P300-based Concealed Information Test has been developed for criminal testing, though field validation remains incomplete. Because P300...
padding Practice
Padding is an alternate term for the irrelevant items in a Known-Solution Peak of Tension test. In some reports, it refers only to the first or last one or two items in the series that serve as buffers.
pain countermeasure Practice
A pain countermeasure is a type of Physical Countermeasure where an examinee covertly self-induces discomfort — biting the tongue, pressing against a sharp object in the shoe, forcing a fingernail into the thumb cuticle — to evoke physiological responses at strategic moments. While spontaneous at...
Paired Testing Examination Techniques
A polygraph approach where two or more examinees involved in a shared event or disputed fact are tested using identical relevant questions. Allows direct comparison of results between participants regarding the same issue. Commonly used in domestic disputes, workplace incidents, and he-said-she-said investigations.
paradigm Practice
A paradigm is an example or model. Experimental paradigms in PDD attempt to explain real-world deception by assessing critical elements and their relationships. The CQT and Concealed Information Test represent two fundamentally different paradigms for approaching deception detection.
parameter Practice
In PDD, parameter denotes a single physiological data channel — Pneumograph, cardiograph, electrodermal, or Plethysmograph. The term distinguishes individual recording channels from the multi-channel polygraph instrument as a whole.
The branch of the autonomic nervous system responsible for "rest and digest" functions, counterbalancing the sympathetic (arousal) system. Parasympathetic activation slows heart rate, reduces blood pressure, and promotes homeostasis. In polygraph testing, the interplay between sympathetic activation (stress response) and parasympathetic recovery provides diagnostically useful cardiovascular data patterns.
parasympathomimetic Physiology
A parasympathomimetic is an agent whose effects mimic parasympathetic nerve stimulation, especially those produced by acetylcholine. Such substances can influence the physiological baselines measured during PDD testing.
Pathometer Instruments
The Pathometer was a recording galvanometer used by Rev. Walter Summers to perform deception tests in the 1930s. Summers conducted testing on hundreds of subjects using the Pathometer and a structured testing procedure that included what would later be known as comparison questions.
Specialised polygraph testing used to monitor convicted sex offenders during probation, parole, or treatment programs. Includes three sub-types: Sexual History Disclosure, Monitoring/Compliance (verification of probation terms), and Maintenance (ongoing periodic testing). Requires additional APA-approved specialised training beyond basic examiner certification.
The scientific term for polygraph examination as defined by ASTM International and the scientific community. PDD is the preferred technical terminology in federal government, academic, and research contexts. Refers to the measurement and analysis of physiological responses to structured questioning to assess the probability of deception.
A polygraph technique presenting the examinee with a series of items (e.g., names, locations, amounts) where only one is crime-relevant. Monitors for a "peak" physiological response at the critical item. Known Peak of Tension (KPOT) uses items known to the examiner; Probing Peak of Tension (PPT) explores unknown details and can help locate evidence or identify co-conspirators.
The Pearson product-moment correlation tests the linear relationship between two sets of interval-level data, producing coefficients from -1 (perfect negative) to +1 (perfect positive). In PDD research, it is used to assess relationships between physiological measures, scoring methods, and decisi...
Per Se Exclusion Legal
A legal rule in certain jurisdictions that categorically bars polygraph evidence from being admitted in court, regardless of the specific circumstances or quality of the examination. Contrasted with jurisdictions that evaluate polygraph admissibility on a case-by-case basis under Daubert or Frye standards. The U.S. Supreme Court in United States v. Scheffer (1998) upheld per se exclusion in military courts.
peripheral nervous system Physiology
The peripheral nervous system consists of nerves and ganglia outside the brain and spinal cord. It includes the somatic (voluntary) and autonomic (involuntary) branches. The autonomic branch — controlling heart rate, breathing, sweating, and blood pressure — produces the physiological signals the...
phalanx Physiology
A phalanx (plural: phalanges) is any bone of the fingers or toes. In PDD, electrodermal sensors are typically attached to the distal phalanx (fingertip) and the Plethysmograph sensor is placed on another finger.
Phasic Response Physiology
A short-duration, stimulus-specific physiological change measured during polygraph testing. Phasic responses occur in reaction to individual questions and are the primary data used for scoring. Distinguished from tonic activity, which represents the overall baseline level. Polygraph analysis relies on phasic response patterns across channels to assess deception.
photopolygraph Instruments
The photopolygraph was an elaborate laboratory polygraph created by C.W. Darrow in the 1930s, recording blood pressure, Skin Resistance, breathing, reaction time, and bilateral hand tremors. Costing over $2,000 and requiring a separate technician, it saw limited field use. Also called the Darrow ...
Physical Countermeasure Practice
A deliberate physical action taken during a polygraph test to manipulate physiological responses, such as tongue biting, toe pressing, muscle tensing, controlled breathing, or anal sphincter contraction. Modern polygraph instruments use activity sensors on the seat and feet to detect physical countermeasure attempts. Examiners are trained to observe and identify these behaviours.
Pinocchio response Theory
The Pinocchio response is a nonexistent lie-specific physiological response. The term is used to highlight a common misconception: the polygraph does not work by detecting a magical \"lying signal.\" Instead it measures differential arousal patterns between question types.
place bar Techniques
A place bar restricts a Comparison Question by specifying a different geographic location from the Relevant Question. For example, if the relevant issue occurred in City A, the comparison might ask about behaviour while living in City B. Research has not found exclusive questions to improve accur...
placebo Practice
In PDD, a placebo refers to mental countermeasures using ritual objects, incantations, or other ineffectual actions that examinees believe will impede the polygraph's ability to detect deception. Like medical placebos, any effects are attributable to suggestion rather than actual efficacy.
An optical sensor typically attached to a fingertip or earlobe that measures blood volume changes using infrared light. Records pulse waveform, heart rate, and peripheral vasoconstriction. Some modern polygraph instruments include a plethysmograph as a supplementary fifth channel alongside the standard pneumograph, EDA, and cardiovascular sensors.
Rubber tubes placed around the examinee's chest (thoracic) and abdomen to measure respiratory activity during a polygraph test. Two pneumograph channels record breathing rate, depth, amplitude, and pattern. Respiratory suppression or changes in breathing pattern following relevant questions can indicate deception. One of the four primary polygraph channels.
polygram Practice
A polygram is the complete graphical recording of physiological data from a polygraph test with required annotations. It is often simply called a polygraph chart.
PolyScore Scoring
A proprietary computerised scoring algorithm developed by Dr. Don Krapohl and colleagues at Johns Hopkins University Applied Physics Laboratory. Uses linear discriminant analysis and Bayesian probability to classify examinees as deceptive or truthful. Integrated into Lafayette and other polygraph instrument platforms. Demonstrated accuracy rates of 85–92% under laboratory conditions.
positive control pair Techniques
A positive control pair combines the subjective truth question and subjective lie question to form a set in the Positive Control Technique, where each question is presented twice — once answered truthfully and once deceptively.
Positive Control Technique Techniques
The Positive Control Technique presents each question twice in succession; the examinee answers truthfully once and deceptively once. Each question serves as its own Comparison Question, eliminating the need for separate probable-lie questions. It uses unique decision rules distinct from standard...
post hoc Practice
Post hoc (Latin: \"after this\") refers to criteria or analyses established after an experiment is completed. Post hoc analyses carry less weight than a priori decisions because they may be influenced by knowledge of the results. See: a posteriori.
Post-Test Interview Practice
The structured interview conducted after polygraph chart collection and initial analysis. The examiner discusses preliminary results with the examinee, explores any areas of concern, provides opportunity for clarification or admissions, and debriefs the examinee on next steps. Results disclosed during post-test remain subject to quality control review.
posttest Practice
The posttest is the final portion of a polygraph examination. It may include debriefing an examinee who passed, or interviewing/interrogating one who failed. The posttest is not part of every technique and plays no role in formulating the physiological data results.
pre-ejection period Instruments
The pre-ejection period (PEP) is the time between ventricular contraction (ECG Q-wave) and when the semilunar valves open to eject blood into the aorta (impedance cardiogram B-wave). Shorter PEPs correlate with sympathetic nervous system arousal. If validated, PEP could become an additional PDD c...
A polygraph examination administered as part of the hiring process, primarily for law enforcement, intelligence, and security positions. Addresses topics such as criminal history, drug use, integrity, truthfulness on the application, and (for federal positions) foreign contacts. Subject to EPPA restrictions in the private sector. Government employers are exempt from EPPA prohibitions.
Pre-Test Interview Practice
The structured interview conducted before polygraph chart collection. During the pre-test, the examiner explains the process, obtains informed consent, gathers background information, discusses the examinee's medical and psychological history, reviews all test questions, and establishes rapport. May last from 30 minutes to 2 hours depending on case complexity.
premature ventricle contraction Physiology
A premature ventricular contraction (PVC) is a heartbeat occurring outside normal rhythm, producing visible distortion in the cardiograph tracing. Examiners must recognise PVCs as artifacts rather than diagnostic responses. Sometimes called extrasystolic beat. See: arrhythmia.
pretest interview Practice
The pretest interview is the first phase of a PDD examination where the examiner and examinee discuss the test procedure, medical history, and test issues. It also prepares the examinee psychologically. Duration ranges from 30 minutes to 2+ hours depending on case complexity. All PDD techniques i...
Primary Involvement Question Techniques
A type of relevant question in the Federal ZCT format that directly asks about the examinee's primary role in the offence (e.g., "Did you shoot John Smith?"). Distinguished from Secondary Involvement Questions (indirect participation) and Evidence Connecting Questions (links to physical evidence). Primary involvement questions are the most direct and diagnostically important relevant questions in a multi-facet test.
primary track Techniques
The primary track is one of the tracks in the Quadri-Track Zone Comparison Technique, containing a Relevant Question paired with a non-current exclusive Probable-Lie Comparison Question for comparison. See: Matte (1996).
Probability Estimate Scoring
A numerical value expressing the likelihood that an examinee is deceptive or truthful, calculated by computerised scoring algorithms such as PolyScore and OSS-3. Probability estimates are derived from logistic regression or discriminant analysis models and provide a more nuanced assessment than simple binary (DI/NDI) classifications. Values are typically expressed as a percentage or decimal between 0 and 1.
Probable-Lie Comparison Question Techniques
A type of comparison question designed so that most examinees will answer "No" even though the truthful answer is likely "Yes" (e.g., "Before age 25, did you ever take anything that didn't belong to you?"). Creates a known or suspected deceptive response for comparison with relevant question responses. The traditional comparison question type in CQT formats.
A Comparison Question Test format that uses probable-lie comparison questions (questions designed so the examinee will likely lie or feel uncertain about their answer). Distinguished from Directed-Lie Tests (DLT) where the examinee is explicitly instructed to lie. PLT is the traditional CQT approach; DLT is considered more standardised and increasingly preferred in modern practice.
pseudorelevant question Practice
A pseudorelevant question is worded to appear relevant to the examinee but does not actually address the issue under investigation. Examples: \"Did you lie to any question on this test?\" or \"Do you intend to answer truthfully?\"
Psychogalvanic Reflex Physiology
The Psychogalvanic Reflex (PGR) is an obsolete term coined by Veraguth (1906) for what is now called the electrodermal response.
psychograph Instruments
A psychograph is a 1930s term for a polygraph consisting of a Pneumograph, sphygmograph, and stimulus marker. Also referred to as the Berkeley Psychograph, the Lee Polygraph, or the cardio-pneumo-psychograph.
Psychological Set Techniques
A concept introduced by Backster describing the examinee's mental focus being directed toward whichever test stimulus poses the greatest perceived threat to their well-being. A guilty examinee's psychological set is directed toward relevant questions; an innocent examinee's toward comparison questions. While the concept has explanatory value, modern polygraph science increasingly favours the more widely understood term salience.
Psychological Stress Evaluator Instruments
The Psychological Stress Evaluator (PSE) was the original voice stress analyser, introduced in 1971 by Dektor Counterintelligence and Security. No longer manufactured, it was the precursor to devices like the CVSA. Independent research found no reliable accuracy for deception detection.
psychopath Practice
A psychopath (antisocial personality) exhibits superficial charm, habitual lying, lack of empathy and remorse, and impulsivity. Popular belief holds psychopaths can defeat the polygraph. However, all research has found guilty psychopaths are detected at rates comparable to guilty non-psychopaths....
Pulse Amplitude Physiology
The magnitude of blood pressure fluctuations with each heartbeat, measured by the cardio cuff during polygraph testing. A decrease in pulse amplitude following a relevant question (vasoconstriction) can indicate a stress response associated with deception. Pulse amplitude is one of the Kircher features scored by modern algorithms.
pulse pressure Physiology
Pulse pressure is the arithmetic difference between systolic and diastolic blood pressure. Changes in pulse pressure during PDD testing reflect cardiovascular responses to psychologically significant stimuli.
pulse transit time Instruments
Pulse transit time (PTT) measures how long a mechanical pulse wave takes to travel between two body points — typically from heart (EKG) to finger. Faster PTT corresponds with greater sympathetic activation. PTT may have future usefulness as a PDD parameter.
punishment theory Theory
Punishment theory proposes that physiological arousal during deception is activated by fear of consequences if detected. It fails to explain why polygraph testing works effectively in the absence of meaningful consequences. See also: fear of detection model.
pupillary response Physiology
Pupillary response is the change in pupil diameter in response to stimuli. Dilation results from sympathetic activation or parasympathetic suppression. Several researchers have investigated pupil dilation as a stress/deception index, and it continues to be of interest in PDD research.
Purposeful Non-Cooperation Practice
Purposeful Non-Cooperation (PNC) is a PDD outcome indicating the examinee used physical countermeasures to defeat the examination. First described by John Reid, PNC is not synonymous with deception, though Reid considered it a reliable indicator of deceptive intent.
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Quadri-Track Zone Comparison Technique Techniques
The Quadri-Track Zone Comparison Technique is a single-issue technique by James Matte extending Backster's method. It has four tracks: primary and secondary (relevant/comparison pairs), the inside track (fear of error/hope of error questions), and the outside track (symptomatic questions).
A process in which a completed polygraph examination (methodology, charts, questions, and scoring) is independently reviewed by a second qualified examiner. QC review strengthens accuracy, identifies scoring errors, ensures procedural compliance with APA standards, and provides a defensible second opinion. Required or recommended by most federal agencies and professional standards.
Question Formulation Practice
The process of constructing polygraph test questions according to established principles. APA standards require that relevant questions be clear, answerable with "Yes" or "No," limited to a single issue, free from legal terminology, and reviewed with the examinee before testing. Proper question formulation is critical to both test validity and examinee comprehension. Poorly worded questions can produce uninterpretable data. See our guide to crafting polygraph questions.
Question Sequence Techniques
The specific order in which questions are presented during a polygraph chart. Different validated techniques prescribe different question sequences — for example, Backster ZCT uses a zone-based pairing structure while the Utah CQT uses a specific alternating pattern. The question sequence affects physiological response dynamics and must follow the protocol of the validated technique being used.
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R-wave peak to carotid incisura Instruments
The R-wave peak to carotid incisura (RWPCI) is a cardiac response measured by the interval between the EKG R-wave (ventricular contraction) and the arrival of the pulse wave at the carotid artery in the neck. It has been investigated as an additional measure of sympathetic arousal in PDD.
One of the earliest polygraph testing formats, using only relevant and irrelevant (neutral) questions without comparison questions. The examiner evaluates whether responses to relevant questions are consistently stronger than to irrelevant questions. Considered less reliable than CQT methods due to lack of a proper comparison stimulus. Still used in some screening contexts but largely replaced for diagnostic testing.
radial artery Physiology
The radial artery is a major artery in the forearm and wrist, and one of the alternate PDD recording sites for cardiovascular activity using the blood pressure cuff.
random assignment Practice
Random assignment places selected research subjects into groups by chance (e.g., coin flip, random number tables). It ensures experimental effects are not due to systematic grouping error. In PDD research, subjects are randomly assigned to innocent or guilty conditions.
random selection Practice
Random selection is a method of extracting research samples from a population so each individual has an equal chance of being selected. True random selection is difficult in PDD research — subjects are often drawn from subgroups (military recruits, college students) that may not represent the bro...
rank order analysis Scoring
Rank order analysis assigns ranks to response intensities within a physiological channel. Methods for the CQT include the Horizontal Scoring System and the Rank Order Scoring System. Ranking responses was first published for the Guilty Knowledge Test in the 1950s.
Rapport Practice
The interpersonal relationship and trust established between the examiner and examinee during the pre-test interview. Effective rapport building puts the examinee at ease, encourages honest disclosure, reduces general anxiety that could contaminate data, and increases the likelihood of obtaining reliable physiological responses. APA training emphasises rapport as a fundamental examiner skill.
A variant of the Comparison Question Test developed by David Raskin at the University of Utah. One of the earliest scientifically validated polygraph testing techniques. Features specific question construction rules, standardised scoring procedures, and directed-lie comparison questions. The Utah CQT has been extensively studied and forms the basis for many modern CQT protocols. APA-validated.
rationalization Practice
Rationalisation is a self-deception defence mechanism where one reinterprets threatening motives as more acceptable ones. PDD examiners watch for rationalisation during the Pre-Test Interview because faulty test questions that empower self-deceit could produce false negative results. No research ...
reaction tracing Scoring
A reaction tracing is the section of a physiological recording where Arousal is apparent — the visible response to a stimulus, as opposed to the baseline or relief sections of the tracing.
recognition test Theory
Recognition tests are knowledge-based polygraph formats — including Peak of Tension, Acquaintance Test, and Concealed Information Test — that determine whether the examinee has knowledge only available to persons directly involved in an incident. They depend on the existence of known facts unknow...
recovery half-time Scoring
Recovery half-time is the interval between the onset of a Phasic Response and its return to half of maximum amplitude. It has been investigated as a diagnostic feature for electrodermal data in automated analysis systems.
Recovery Time Physiology
The duration required for a physiological measure to return to baseline following a stimulus-evoked response. In EDA, recovery time (or recovery half-time) refers to how long the conductance takes to decline to 50% of its peak amplitude. Slower recovery following relevant questions may indicate heightened arousal and is used as a supplementary scoring feature in some analysis methods.
Red Zone Techniques
In Backster's Zone Comparison Test, the portion of the question sequence containing the relevant questions that directly address the issue under investigation. Deceptive examinees are expected to show their strongest physiological responses in the Red Zone. See also Green Zone and Black Zone.
regression analysis Scoring
Regression analysis mathematically models relationships between variables and is used for prediction. In PDD, at least one Algorithm uses a form of regression to combine physiological measures for optimal decision accuracy.
A pivotal figure in polygraph history who introduced the comparison question to polygraph testing in 1947, fundamentally changing the field. Developed the Reid Control Question Technique (CQT), which became the basis for most modern polygraph methods. Founded the Reid College of Detection of Deception (later John E. Reid & Associates) in Chicago. His work established the framework that Backster and others later refined.
Relevant Issue Gravity Theory
Relevant Issue Gravity (RIG) is a theory by Avital Ginton (2009) proposing that the relevant issue's qualities create a \"gravitational\" force on the guilty examinee's attention — binding it to relevant questions in a way not experienced by the innocent. Unlike older theories, RIG does not rely on...
A question in a polygraph test that directly addresses the issue under investigation (e.g., "Did you take the missing money?" or "Have you had sexual contact with anyone other than your partner since your marriage?"). Responses to relevant questions are compared with responses to comparison and irrelevant questions to determine the presence or absence of deception.
relief tracing Scoring
A relief tracing is the section of a physiological recording where recovery from arousal is apparent — the return toward baseline after a response.
respiratory cycle time Physiology
Respiratory cycle time (RCT) is a diagnostic feature calculated by comparing the breathing cycle duration before and after question presentation. Lower ratios indicate longer cycles after stimulation, reflecting sympathetic arousal. RCT evaluation presupposes stable baseline respiratory patterns.
respiratory sinus arrhythmia Physiology
Respiratory sinus arrhythmia (RSA) describes normal heart rate variations directly related to breathing — slower during inspiration, faster during expiration. RSA contributes to the undulating waveform sometimes visible in the cardiograph channel.
Respiratory Suppression Physiology
A decrease in breathing amplitude, rate, or regularity following a relevant polygraph question compared to baseline or comparison question responses. Respiratory suppression is one of the primary Kircher features scored in polygraph analysis and is considered a reliable indicator of psychophysiological stress associated with deception.
response onset window Scoring
The response onset window is the time period after question onset during which physiological responses are considered for analysis and scoring. Responses occurring outside this window are not attributed to the test question.
Retesting Practice
The practice of conducting a second polygraph examination after an initial test produces an inconclusive result or when data quality was insufficient. APA standards provide guidelines for when retesting is appropriate, typically requiring a minimum interval between tests. Retesting should use the same validated technique and question format where possible.
rise time Scoring
Rise time is the period between the start of a physiological response and its greatest amplitude. It is one of several temporal characteristics used in automated analysis algorithms for PDD data.
A measurement feature used in automated polygraph scoring that calculates the total path length of the respiratory tracing over a defined time window. Shorter respiration line length following a relevant question (indicating suppression or holding of breath) is associated with deception. Used as an automated alternative to visual pattern recognition in manual scoring of pneumograph data.
A graphical plot used in polygraph research to evaluate the diagnostic performance of a scoring method across all possible cut-score thresholds. The ROC curve plots sensitivity (true positive rate) against 1 − specificity (false positive rate). The area under the ROC curve (AUC) provides a single measure of overall discriminative ability — values closer to 1.0 indicate better performance. Used to compare scoring algorithms and validate new techniques.
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S-K-Y Techniques
S-K-Y (Suspect, Know, You) is a standardised Zone Comparison Technique format under the Backster Zone Comparison Technique umbrella. It broadens a single-issue test to include secondary involvement and knowledge questions alongside direct-involvement questions. Rarely used today.
The first relevant question in a polygraph test sequence, which is expected to produce a strong orienting response simply because it introduces the relevant topic for the first time. Because this initial response reflects novelty rather than deception, the sacrifice relevant question is typically not scored. It "sacrifices" diagnostic value to absorb the orienting effect, allowing subsequent relevant questions to produce more diagnostically meaningful data.
Salience Physiology
The psychological significance or personal relevance of a stimulus (question) to the examinee, which drives the magnitude of physiological response. In polygraph theory, relevant questions are more salient to deceptive examinees (producing larger responses) while comparison questions are more salient to truthful examinees. The modern scientific term replacing the older concept of "psychological set."
A landmark U.S. Supreme Court case that upheld Military Rule of Evidence 707, banning polygraph evidence in military courts-martial. While the majority ruling maintained the per se exclusion rule, Justice Kennedy's concurring opinion (joined by three other justices) expressed doubt about the wisdom of blanket exclusion, leaving the door open for future challenges. The decision left admissibility to individual jurisdictions in civilian courts.
scientific cradle Instruments
The scientific cradle was a device built by Angelo Mosso (1896) to record respiratory and cardiovascular responses to fear. A subject lay on a balanced platform, and the shifting of blood concentration and breathing undulations were recorded on a smoked drum.
screening examination Techniques
A screening examination is a polygraph test conducted without a specific reported incident to investigate whether the examinee has withheld information about specified behaviours. Its strength is developing information unobtainable by other means; its limitation is lower accuracy than specific-is...
Screening Opinion Results
The examiner's professional judgment in a multi-issue screening polygraph (as opposed to a diagnostic single-issue test). Expressed as SR (Significant Response) or NSR (No Significant Response) rather than DI/NDI. Screening opinions are less specific than diagnostic opinions because they address multiple issues simultaneously.
Searching Peak of Tension Techniques
A Searching (or Probing) Peak of Tension (SPOT) test is used when the examiner does not know the critical item, aiming to uncover information concealed by a guilty examinee — such as locations of stolen goods, bodies, or amounts stolen. There is no published research supporting the SPOT.
Secondary Involvement Question Techniques
A type of relevant question in the Federal ZCT format that asks about indirect involvement in the offence (e.g., "Did you help plan the theft?" rather than "Did you commit the theft?"). Used alongside primary involvement and evidence connecting questions to comprehensively address an investigation within a single polygraph examination.
secondary track Techniques
The secondary track in the Quadri-Track Zone Comparison Technique contains a Relevant Question paired with a non-current exclusive Probable-Lie Comparison Question. See: Matte (1996).
Sensitivity Results
The quantitative ability of a polygraph technique or scoring method to correctly identify deceptive examinees (true positive rate). High sensitivity means fewer deceptive individuals escape detection (fewer false negatives). Measured as TP / (TP + FN). Balanced against specificity in validated scoring systems.
sensory nerves Physiology
Sensory nerves (afferent nerves) carry impulses from the body's periphery to the central nervous system. They transmit the sensory input — including hearing test questions — that initiates the cognitive processing leading to polygraph-measurable responses.
serrated breathing pattern Physiology
A serrated breathing pattern occurs when the examinee's pulse is visible in the respiratory tracing due to sensor proximity to the heart, creating a \"saw-tooth\" appearance on the breathing waveform.
Seven-Position Scoring Scoring
A detailed numerical scoring method using values from −3 to +3 to represent the magnitude of response difference between relevant and comparison questions. +3 indicates a much stronger comparison response (suggesting truthfulness) while −3 indicates a much stronger relevant response (suggesting deception). The traditional manual scoring system used in most CQT formats.
A specialised area of polygraph practice involving the testing of convicted sex offenders as part of supervision, treatment, or community safety programs. Encompasses sexual history disclosure tests, monitoring/compliance tests, and maintenance tests. Requires additional APA-approved training and adherence to specific PCSOT standards. Used in all 50 U.S. states and in several countries internationally. See also PCSOT.
A sub-type of PCSOT polygraph testing in which the convicted sex offender is tested regarding the completeness and accuracy of their disclosed sexual history. Conducted as part of treatment programs to ensure full disclosure of past offending behaviour. Requires specialised PCSOT examiner training.
sexual offender monitoring Practice
Sexual offender monitoring uses the polygraph to verify that sex offenders on parole or probation comply with their release conditions. It is a key component of Post-Conviction Sex Offender Testing programmes.
signal detection theory Scoring
Signal detection theory (SDT) quantifies a test's capacity to discriminate between signal (deception) and noise (truthfulness). Using SDT, optimal cutting scores can be calculated balancing the costs and benefits of different error types. It is foundational to ROC Curve analysis in PDD.
signal value Theory
Signal value is the perceived significance of a stimulus to an organism. In PDD, greater signal value produces greater physiological responses. A CQT aims to make the external significance of relevant and comparison questions appear equal, while their internal significance varies between truthful...
The ratio of meaningful physiological signal to background noise or artifact in a polygraph recording. Higher SNR produces cleaner data and more reliable scoring. Factors affecting SNR include sensor quality, proper attachment, environmental noise, examinee movement, and instrument calibration. Digital polygraph instruments generally achieve superior SNR compared to analog predecessors.
silent answer test Techniques
The silent answer test (SAT) directs examinees to answer internally rather than verbally, avoiding respiratory distortions from speech. Some examiners instruct examinees to nod/shake their heads (SAT Nod). The SAT can also help detect certain Countermeasures.
Silent Talker Techniques
Silent Talker is an experimental automated credibility assessment system that analyses body movements and facial gestures from recorded video using an Artificial Neural Network. Evidence for its accuracy is limited. See: Rothwell et al. (2006).
A polygraph examination that focuses on one specific target issue or event (e.g., "Did you steal the money on March 15th?"). Considered more accurate than multi-issue screening tests because attention is focused on a single topic. Results are reported as DI, NDI, or INC. All APA-validated diagnostic techniques are single-issue or event-specific formats. Recommended for legal, evidentiary, and investigative applications.
situational comparison question Practice
A situational comparison question is used in the Modified Relevant/Irrelevant technique. Rather than a question the examinee is deceiving about, it addresses how the examinee is connected to the crime (e.g., having had access to stolen money). It allows truthful examinees to respond to a crime-re...
skin conductance Physiology
Skin conductance (SC) is a broad term for two exosomatic electrodermal phenomena: skin conductance level (tonic/baseline) and skin conductance response (phasic/stimulus-evoked). Modern polygraphs typically measure SC rather than Skin Resistance.
skin conductance level Physiology
Skin conductance level (SCL) is the tonic (baseline) measure of skin conductance — the overall conductivity of the skin at any given moment, reflecting general arousal state.
skin conductance response Physiology
Skin conductance response (SCR) is the phasic change in skin conductance elicited by a stimulus. SCR is one of the most diagnostic features evaluated in PDD chart analysis.
skin potential Physiology
Skin potential (SP) is an endosomatic electrodermal measure — voltage generated internally by the dermis without external current. Though not currently standard in PDD, preliminary research has shown SP to be as diagnostic as exosomatic measures.
skin potential level Physiology
Skin potential level (SPL) is the tonic (baseline) electropotential of the skin.
skin potential response Physiology
Skin potential response (SPR) is an endosomatically produced electrodermal response, measured between the forearm and the hypothenar eminence. It is of research interest as a potential additional PDD parameter.
An older method of measuring electrodermal activity that records the skin's resistance to electrical current (measured in ohms or kilohms), as opposed to the modern conductance method. Skin resistance decreases when sweat gland activity increases. While older polygraph instruments used resistance measurements, modern digital systems predominantly use the conductance metric (measured in microsiemens).
skin resistance level Physiology
Skin resistance level (SRL) is the tonic (baseline) level of electrical resistance of the skin.
skin resistance response Physiology
Skin resistance response (SRR) is the phasic change in skin resistance measured when the skin's electrical resistance drops in response to a stimulus.
smoked drum recording Instruments
A smoked drum recording was an early method of recording physiological data. A cylinder wrapped in soot-covered paper rotated against a stylus at a controlled speed, creating tracings preserved with shellac varnish. It was the precursor to continuous strip chart recording used in later polygraphs.
smooth muscles Physiology
Smooth muscles are involuntary, non-striated muscles involved in autonomic functions — found in the bladder, intestines, and blood vessels. In polygraph context, smooth muscle control of blood vessel diameter (Vasoconstriction/vasodilation) produces the cardiovascular changes recorded by the card...
Spearman Rank Correlation Scoring
The Spearman Rank Correlation tests correlation between ordinal-level data. In PDD, it can assess inter-rater reliability by comparing the rankings different evaluators assign to question responses.
Specificity Results
The quantitative ability of a polygraph technique or scoring method to correctly identify truthful examinees (true negative rate). High specificity means fewer truthful individuals are falsely accused (fewer false positives). Measured as TN / (TN + FP). OSS-3 and ESS demonstrate balanced sensitivity and specificity.
sphygmograph Instruments
A sphygmograph is an instrument for graphically recording arterial pulse and blood pressure. It is the technically precise term for the cardiograph channel in PDD.
sphygmomanometer Instruments
A sphygmomanometer is the aneroid gauge that registers air pressure in the polygraph's cardiovascular sensor system. Changes in the closed system signal relative blood volume changes at the recording site on the examinee.
spontaneous countermeasures Practice
Spontaneous countermeasures are unplanned, unrehearsed Countermeasures attempts. Laboratory studies have consistently shown them to be ineffective — examinees attempting countermeasures without specific training and feedback generally fail to defeat the polygraph.
spontaneous response Physiology
A spontaneous response is any physiological reaction not associated with an identifiable stimulus. High frequency of spontaneous responses indicates elevated general Arousal. Also called a non-specific response.
spot analysis Scoring
Spot analysis is the numerical evaluation of a Relevant Question by comparing it to an adjacent Comparison Question. The \"spot\" represents the relevant question's location in the question series.
spot responder Scoring
A spot responder is an unproven concept suggesting some examinees respond physiologically to a question based on its position in the sequence rather than its content. Some techniques rotate relevant question positions between charts to address this concern.
The total numerical score for a single specific relevant question across all charts. The Spot-Score Rule in the ESS evaluates whether any individual relevant question reaches the deception threshold, even if the Grand Total does not. This two-stage approach (Grand Total + Spot Score) improves accuracy for cases where deception is limited to one specific question.
Used in multi-issue screening tests. Indicates significant physiological responses to one or more relevant questions, suggesting potential deception on those specific issues. The screening equivalent of DI in diagnostic testing. Does not specify which question triggered the response — follow-up diagnostic testing is typically recommended.
stabile Practice
Stabile means resistant to change — the opposite of labile. Stabile PDD tracings show minimal spontaneous activity and narrow amplitude ranges, suggesting low baseline arousal.
staircase respiration Physiology
Staircase respiration is a breathing pattern where inhalation peaks progressively rise (ascending staircase) or fall (descending staircase) with each cycle. The descending version has been found diagnostic in at least one study.
standard deviation Scoring
Standard deviation is a statistical measure of score dispersion — the square root of the average squared deviation from the mean. In PDD research, it quantifies the variability in test scores, physiological measurements, and Accuracy estimates across studies.
The comprehensive set of professional standards established by the American Polygraph Association governing all aspects of polygraph examination practice. Covers testing environment, instrumentation, question formulation, scoring methods, reporting, data retention, continuing education, and ethical conduct. Compliance is mandatory for APA members and qualified examiners.
Statement Verification Test Practice
A polygraph format where the examinee prepares a written statement containing their account of the facts. The polygraph test then verifies the truthfulness of the overall statement rather than testing individual elements separately. Classified as a multiple-issue examination.
statistical significance Scoring
Statistical significance indicates an experimental result unlikely to have occurred by chance. In PDD, conventional thresholds are p < 0.05 and p < 0.01 — meaning less than a 5% or 1% probability the result is due to chance alone.
A brief polygraph demonstration administered at the beginning of an examination to show the examinee the instrument can detect deception. The examinee is asked to lie to a known question (e.g., choose a number, then deny it). Builds examiner confidence in sensor placement and demonstrates the process. Sometimes called a "card test" or "number test."
Stimulus-Response Theory Physiology
The theoretical framework underlying polygraph testing which holds that specific stimuli (test questions) produce measurable physiological responses, and that the magnitude and pattern of these responses differ systematically between deceptive and truthful examinees. Deception-related stimuli are more salient to deceptive individuals, producing stronger ANS activation compared to comparison stimuli.
A formal written agreement between parties in a legal proceeding to submit to polygraph testing and to accept the admissibility of results in court. Stipulations typically specify the examiner, technique, issues to be tested, and how results will be used. Stipulated polygraph evidence is admissible in many U.S. jurisdictions where un-stipulated polygraph results would be excluded.
Stoelting Company Instruments
A manufacturer of polygraph instruments and psychological testing equipment. Stoelting's computerised polygraph systems are used in law enforcement, government, and private practice. One of the four major polygraph instrument manufacturers alongside Lafayette, Limestone, and Axciton.
straight-through test Techniques
A straight-through test (ST) is a Reid polygraph test using the standard question sequence, conducted before other sequence variations such as the Mixed Question Test.
strain gauge Instruments
A strain gauge is a sensor registering changes in the dimensions of a body. In PDD, pneumatic strain gauges placed around the thorax or abdomen record breathing movements.
striated muscles Physiology
Striated muscles include all skeletal muscles (voluntary contractions) and cardiac muscle (involuntary). The Autonomic Nervous System does not directly control striated skeletal muscle, which is why the polygraph focuses on involuntary autonomic responses rather than voluntary muscular activity.
stroke volume Physiology
Stroke volume (SV) is the amount of blood ejected from the heart with each beat. Changes in stroke volume contribute to the blood pressure and pulse wave variations recorded by the polygraph's cardiovascular channel.
strong relevant question Practice
A strong relevant question goes directly to the core of the matter under investigation (\"Did you do it?\"). It contrasts with moderate-strength relevant questions that address knowledge, complicity, evidence connections, alibis, or secondary involvement.
subjective lie/truth question Practice
In the Positive Control Technique, each question is presented twice. The first presentation (where the examinee admits the offence) is the subjective lie question; the second (where they deny it) is the subjective truth question.
Subtotal Score Scoring
The numerical score for a single relevant question within a single chart. Individual subtotals are combined to produce spot scores (per question across all charts) and grand totals (all questions across all charts). Analysis of subtotal score distributions helps validate scoring systems and optimise cut-scores for decision rules.
successive hurdles approach Techniques
The successive hurdles approach is a two-stage screening strategy: start with a multiple-issue test (high sensitivity, catches most deceptive examinees), then follow up any flagged issues with a focused Single-Issue Test (high specificity, reduces false positives). The net result is better accura...
Summers, Walter Practice
Rev. Walter Summers was an early deception testing researcher who used an electrodermal device (the Pathometer) and structured test series including what he called \"emotional standards\" — the earliest known version of comparison questions. See: Summers (1939).
Supervised Experience Practice
The period of supervised practice required after completing an APA-accredited training program, during which a new examiner conducts polygraph examinations under the guidance of an experienced supervisor. Typically requires 25–200 examinations depending on the licensing jurisdiction. The supervisor reviews cases, scoring, and reports to ensure competency before the trainee practises independently.
surreptitious breathing tracing Practice
A surreptitious breathing tracing is recorded when the examinee is unaware — typically just before or after testing. It provides a Baseline for assessing whether the examinee altered their breathing during the test, which could indicate Countermeasures.
sympathetic chain Physiology
The sympathetic chain is a system of 21–22 pairs of ganglia in the thoracic and abdominal areas where pre- and postganglionic sympathetic neurons synapse. One exception: there is no postganglionic sympathetic nerve to the adrenal medulla, which receives direct preganglionic innervation.
Sympathetic Response Physiology
Activation of the sympathetic branch of the autonomic nervous system, producing the physiological changes measured by the polygraph: increased heart rate, elevated blood pressure, increased sweat gland activity, and changes in respiration. Sympathetic activation in response to relevant questions may indicate deception-related stress.
sympathomimetic Physiology
A sympathomimetic is a drug that mimics the action of sympathetic nerves or their neurotransmitters, potentially influencing the physiological responses measured during PDD testing. Such medications are of concern as potential pharmacological countermeasures.
A question type introduced by Backster designed to identify whether the examinee has an unresolved concern about an issue not covered by the test (e.g., "Is there something else you're afraid I'll ask you about?"). Placed in the Black Zone of the ZCT. Intended to detect "outside issues" that could contaminate responses to relevant questions. Research on the effectiveness of symptomatic questions has been mixed.
synapse Physiology
A synapse is the junction between neurons where neurotransmitters are released to transmit signals. Synaptic transmission is fundamental to all nervous system signalling, including the autonomic pathways that produce polygraph-measurable responses.
systole Physiology
Systole is the contraction phase of the cardiac cycle. Left ventricular systole pumps blood into the aorta, producing the highest point in the cardiograph pulse wave. It is subdivided into pre-ejection, ejection, and relaxation periods.
systolic blood pressure Physiology
Systolic blood pressure is the maximum force blood exerts against arterial walls during ventricular contraction, expressed in mmHg. It represents the peak of the blood pressure cycle visible in polygraph cardiovascular recordings.
T
tachycardia Physiology
Tachycardia is an abnormally rapid heartbeat (>100 bpm). In PDD, tachycardia may signal pharmaceutical Countermeasures, extreme anxiety, or underlying medical conditions. While not diagnostic of deception itself, examiners monitor heart rate as context for cardiovascular channel interpretation.
tachypnea Physiology
Tachypnea is rapid, usually shallow breathing. In polygraph testing, tachypnea may indicate anxiety, a medical condition, or an attempt to manipulate respiratory recordings.
Target Issue Techniques
The specific matter or allegation that a polygraph examination is designed to address. In single-issue (diagnostic) testing, there is one target issue; in multi-issue screening, there may be several. Clear definition of the target issue before the examination is essential to proper question formulation and ensures the examinee understands exactly what is being tested.
The process of analysing recorded physiological data from a polygraph examination to reach a diagnostic or screening opinion. Includes manual scoring (numerical or global), automated algorithm scoring, or a combination. APA standards require the use of validated TDA methods. Evidence-based TDA has significantly improved polygraph accuracy and reliability.
A screening polygraph format specifically designed for counterintelligence testing, addressing espionage and sabotage issues. An APA-validated technique used by U.S. federal agencies for security screening of personnel with access to classified information.
test Practice
In PDD, test differentiates a single running of a question series (also called a chart) from the examination, which is the entire PDD process. \"Test\" also refers to specialised procedures like the Yes Test or stimulation test. Using \"test\" to mean \"technique\" (e.g., \"Zone Comparison Test\") is tec...
Test-Retest Reliability Techniques
A measure of the consistency of polygraph results when the same examinee is tested on the same issue at different times. High test-retest reliability indicates the technique produces stable results. APA standards provide guidelines for when retesting is appropriate, including minimum intervals between examinations and protocols for managing prior test knowledge.
Theft & Employee Testing Practice
Polygraph examinations conducted to investigate specific incidents of theft, embezzlement, fraud, or property loss in workplace settings. Under EPPA, private employers may request employee polygraph testing only when an investigation involves economic loss or injury to the employer's business, and specific procedural safeguards must be followed. Government employers are exempt from EPPA restrictions.
thenar eminence Physiology
The thenar eminence is the prominence on the palm at the base of the thumb. Along with the hypothenar eminence, it is one of the optimal recording sites for electrodermal activity due to its high concentration of eccrine sweat glands.
Therapeutic Polygraph Practice
A polygraph examination conducted as part of a treatment or therapy program, most commonly in sex offender treatment or addiction recovery. Used to support the therapeutic process by verifying compliance, encouraging accountability, and facilitating disclosure. The examiner typically coordinates with the treating therapist or probation officer. Distinct from investigative or evidentiary polygraph testing.
thermal imaging Techniques
Thermal imaging uses infrared cameras to record radiant energy from the body. Facial thermal pattern changes correlate with physiological arousal, and preliminary evidence suggests thermal imaging can discriminate between truthful and deceptive individuals above chance. The technology is non-cont...
Thoracic Breathing Physiology
Respiratory activity measured by the upper (thoracic) pneumograph tube placed around the examinee's chest. Thoracic and abdominal breathing patterns are recorded on separate channels because stress-related respiratory changes may manifest differently in the chest versus abdomen. Both channels are scored independently, and discrepancies between them can indicate countermeasure attempts.
thoraco-lumbar division Physiology
The thoracolumbar division is an anatomical classification of the sympathetic branch of the Autonomic Nervous System, representing where sympathetic nerves exit the spinal cord through the thoracic and lumbar segments. It contains the 21–22 pairs of ganglia forming the sympathetic chain.
Three-Position Scoring Scoring
A simplified numerical scoring method using only three values: +1 (comparison response stronger), 0 (equal/no significant difference), and −1 (relevant response stronger). Used in the Empirical Scoring System (ESS). Research shows three-position scoring produces comparable accuracy to the more complex seven-position system while being easier to learn and more reliable across scorers.
time bar Techniques
A time bar restricts a Comparison Question to exclude the time period of the incident under investigation (e.g., \"Before age 25, did you ever...\"). Research has not supported the hypothesis that exclusive questions improve accuracy over non-exclusive versions. See also: category bar, place bar.
The overall baseline level of physiological activity in a given channel, as opposed to phasic (stimulus-specific) responses. Tonic levels represent the examinee's general state of arousal. While phasic responses are the primary focus of polygraph scoring, tonic shifts (e.g., sustained elevation in skin conductance) can provide supplementary diagnostic information.
tonic change Physiology
A tonic change is the shifting of tonic level to a new baseline, occurring slowly compared to phasic responses.
Tonic Level Physiology
The overall resting level of a physiological measure (e.g., baseline electrodermal conductance, resting blood pressure, or normal breathing rate) before stimulus-related changes occur. In polygraph analysis, phasic responses (stimulus-specific changes) are measured against the tonic level. Significant shifts in tonic level during an examination may indicate general arousal, fatigue, or medication effects.
tonic response Physiology
A tonic response is a slow shift in baseline level in response to changing conditions (e.g., temperature, posture). Some examiners consider tonic trends diagnostic in Peak of Tension tests, though research evidence is limited.
total chart minutes concept Techniques
The total chart minutes concept (TCMC) was offered by Cleve Backster (1963) to account for possible variation in habituation rates across physiological channels over time. It has not received much research attention and is not currently taught in the field.
tracing average Scoring
The tracing average is the section of a physiological recording used as a comparative baseline, showing no indications of arousal. Also called the baseline level.
tracing distortion Scoring
Tracing distortion is contamination of a physiological recording, typically by examinee movements. Also called artifact.
track Techniques
A track is a pair of polygraph test questions used for evaluative purposes — a concept central to the Quadri-Track Zone Comparison Technique. See: Matte (1996).
Transducer Physiology
An electronic device in the polygraph instrument that converts physiological signals (air pressure from pneumograph tubes, electrical conductance from finger plates, pressure from cardio cuff) into electrical signals that can be digitised, displayed, and recorded. The accuracy and sensitivity of transducers directly affects polygraph data quality.
Traube-Hering-Mayer wave Physiology
The Traube-Hering-Mayer (THM) wave is a rhythmic low-frequency fluctuation (~0.1 Hz) in heart rate linked to blood pressure feedback loops involving the carotid baroreceptors. It contributes to variability expressed in respiratory sinus arrhythmia and is relevant to understanding cardiovascular p...
Trauma-Informed Testing Practice
A polygraph examination approach that accounts for the examinee's history of trauma, abuse, or psychological distress. APA standards require examiners to use sensitivity in question formulation, provide appropriate pre-test preparation, and avoid re-traumatisation. Trauma-informed techniques are particularly important in PCSOT, sexual assault investigations, and domestic cases.
tremograph Instruments
A tremograph is an instrument for recording tremors. Aleksandr Luria proposed in the 1930s that trembling could index emotional arousal for deception detection, based on his conflict theory that incompatible emotions affect bodily responses.
true negative Scoring
A true negative is a correct PDD decision that the examinee is not deceptive — an accurate outcome of truthfulness. See also: Specificity.
true positive Scoring
A true positive is a correct PDD decision that the examinee is deceptive — an accurate outcome of deception detection. See also: Sensitivity.
Two-Stage Decision Rules Scoring
A decision framework in the Empirical Scoring System (ESS) that uses two sequential rules: Stage 1 applies the Grand Total Rule to all questions combined; Stage 2 applies the Spot-Score Rule to individual questions. Two-stage rules improve criterion accuracy by catching cases where deception is concentrated on a single relevant question that might not reach the grand total threshold alone.
Two-Stage Rules Scoring
A decision framework used in the Empirical Scoring System (ESS) that applies two sequential tests to determine the final classification. Stage One applies the Grand Total Rule (summing all scores). If the Grand Total falls within the inconclusive range, Stage Two applies the Spot-Score Rule to check if any single relevant question exceeds the deception threshold. This two-stage approach reduces inconclusive rates while maintaining accuracy.
type I error Scoring
A Type I error is the probability of rejecting a true null hypothesis — incorrectly concluding deception when the examinee is truthful. In PDD, this is a false positive result. Denoted as α (alpha).
type II error Scoring
A Type II error is the probability of not rejecting a false null hypothesis — failing to detect deception when it is present. In PDD, this is a false negative result. Denoted as β (beta).
U
An alternative term for probable-lie comparison questions, emphasising that the examinee is not explicitly instructed to lie (unlike directed-lie questions). The examinee's deception to these questions is expected but not directed by the examiner. The term is used in some academic literature to clarify the distinction between directed-lie and probable-lie methodologies.
The United States Army Military Police School (USAMPS) was the former instruction centre for U.S. federal PDD examiners from 1951 through 1986. Now called the National Center for Credibility Assessment.
United States v Frye Legal
United States v. Frye (1923) was the first case to consider deception test results as evidence. The Frye Rule stated expert testimony based on a scientific technique is inadmissible unless \"generally accepted as reliable.\" This excluded polygraph evidence for decades until superseded by the Daube...
Utah Probable Lie Technique Techniques
The Utah Probable Lie Technique (UPLT) is a CQT format developed at the University of Utah from the 1970s. Distinctive features include: relevant questions not bracketed by comparison questions; inclusion of the photoplethysmograph; rotating comparison questions; up to five charts; and symmetric ...
A three-relevant-question diagnostic polygraph technique developed at the University of Utah by David Raskin and colleagues. An APA-validated format considered one of the most researched comparison question techniques. Forms the basis for the Directed Lie Test (DLT) variant and the Computerized Polygraph System (CPS) scoring algorithm. Widely used in criminal investigation and research settings.
Utility Legal
The practical value or usefulness of polygraph testing in achieving its intended purpose, such as deterring espionage, encouraging disclosures, resolving allegations, or protecting the innocent. Utility is distinct from accuracy — a technique may have utility even when accuracy is imperfect if it prompts admissions, deters misconduct, or provides investigative leads. The NAS report (2003) acknowledged polygraph utility while questioning some accuracy claims.
V
vagal tone Physiology
Vagal tone measures parasympathetic influences on the heart via variability in inter-beat intervals. This variability, driven by respiratory sinus arrhythmia, fluctuates with breathing. It has been investigated as an alternative stress measure in PDD.
vagus nerve Physiology
The vagus nerve is the tenth cranial nerve providing parasympathetic innervation to the heart and other visceral organs. Its activity helps regulate heart rate — the interplay between vagal (slowing) and sympathetic (accelerating) influences produces the cardiovascular patterns polygraphs record.
Validated Technique Practice
A polygraph testing format that has undergone sufficient peer-reviewed scientific research to demonstrate acceptable levels of accuracy, sensitivity, and specificity. The APA meta-analytic survey (2011) identifies 14 validated techniques. Only validated techniques may be used for diagnostic or screening purposes under APA standards. Techniques lacking validation evidence (e.g., AMGQT, Marcy technique) are placed on "stand-down" pending further research.
The degree to which a polygraph technique or scoring method accurately measures what it claims to measure — namely, the presence or absence of deception. Construct validity addresses whether the underlying theoretical model is sound; criterion validity measures how well results match independently confirmed ground truth. APA standards require the use of techniques with demonstrated validity through published peer-reviewed research.
Valsalva's maneuver Physiology
The Valsalva manoeuvre involves forced exhalation against a closed glottis, increasing internal pressure. This produces a short-term blood pressure increase and often an electrodermal response. Because it directly affects polygraph channels, it is classified as a Physical Countermeasure when perf...
variable Practice
In behavioural science, a variable is an element that influences or is influenced by something. In PDD, key variables include Habituation (affects responsivity), Base Rate (affects overall accuracy), and examiner skill (affects decision quality).
Variance Scoring
A statistical measure of the spread or dispersion of physiological response scores within a polygraph data set. Analysis of variance (within-subject and between-subject) helps determine whether observed response differences between relevant and comparison questions are statistically significant. Scoring algorithms use variance estimates to set optimal decision thresholds and calculate confidence intervals.
Vasoconstriction Physiology
A narrowing of blood vessels resulting in reduced blood flow and decreased pulse amplitude, measured by the cardio cuff or plethysmograph during a polygraph test. Vasoconstriction following relevant questions is one of the physiological indicators of stress and potential deception. Included as a Kircher feature in automated scoring algorithms.
vasodilation Physiology
Vasodilation is the expansion of blood vessels, increasing blood flow to a body region. Along with Vasoconstriction, vasodilation is regulated by the Autonomic Nervous System and contributes to the cardiovascular changes recorded by the polygraph.
A sensor measuring blood volume changes in the fingertip or earlobe. Records pulse amplitude and vasomotor constriction patterns. Constriction (reduced pulse amplitude) following relevant questions can indicate deception. An optional fifth channel in some modern polygraph instruments, supplementing the standard four channels.
ventilation Physiology
Ventilation is the regular movement of the chest cavity during breathing. In physiology, \"ventilation\" refers to the mechanical act of breathing (chest expansion/compression), while \"respiration\" technically refers to gas exchange in the lungs. Polygraph pneumographs record ventilation.
vertical scoring system Scoring
The vertical scoring system evaluates each spot individually by comparing relevant and comparison question responses. It is used in the ZCT exploratory and S-K-Y tests. The term contrasts with rank order analysis, which compares responses across the full question series.
voice stress analysis Techniques
Voice stress analysis (VSA) encompasses technologies claiming to detect deception through vocal signal analysis, typically in the 8–10 Hz microtremor range. Devices include the CVSA, LVA, and PSE. No independent scientific assessment has validated any VSA device for credibility assessment. The U....
voir dire Practice
Voir dire (French: \"to say the truth\") is the legal process of questioning prospective jurors to exclude those with biases. In PDD contexts, voir dire may involve expert testimony about polygraph methodology when admissibility of polygraph evidence is being considered.
The Chief of Police of Berkeley, California, who supported John Larson's development and application of the first polygraph instrument in law enforcement in the 1920s. Vollmer is widely regarded as the father of modern policing and championed the use of scientific methods in criminal investigation, including polygraph testing, fingerprinting, and forensic analysis.
A technology that claims to detect deception by analysing micro-tremors in the human voice. Not a polygraph technique. Not validated by the APA or any recognised scientific body. Multiple peer-reviewed studies show VSA performs no better than chance at detecting deception. Examiners and consumers should be aware that VSA-based "lie detector" services are not legitimate polygraph examinations.
W
Weighted Score Scoring
A numerical polygraph score in which different physiological channels are given different mathematical weights based on their demonstrated diagnostic value. For example, in some algorithms, EDA features receive higher weights than respiratory features because research shows EDA has the strongest single-channel correlation with deception. Weighting schemes are derived from regression analysis of confirmed case databases.
Wheatstone bridge Instruments
The Wheatstone bridge was early electrical circuitry used to detect electrodermal activity. It employed a null-type resistance-measuring circuit comparing the examinee's skin resistance against known resistors. Modern polygraph instruments use more sophisticated measurement approaches.
An American psychologist credited with developing the systolic blood pressure deception test, a precursor to the modern polygraph. His work on blood pressure changes during questioning was presented in the landmark Frye v. United States case (1923). Marston also created the comic character Wonder Woman, whose Lasso of Truth was inspired by his lie detection work. His wife Elizabeth Marston and assistant Olive Richard contributed significantly to the research.
Winter, John Practice
John Winter was the earliest known developer of a scoring system for interpreting polygraph recordings in deception detection (1936). His method did not come into wide use and is of historical interest only.
Workplace Testing Legal
Polygraph examinations conducted in employment contexts, including pre-employment screening for government positions, specific-incident investigations of theft or fraud in private businesses, and compliance monitoring. Subject to EPPA regulations in the U.S. private sector. Government employers, security firms, and pharmaceutical companies have specific exemptions under federal law.
X
A condition of abnormal dryness of the mouth caused by reduced saliva production, often associated with anxiety, certain medications, or medical conditions. While not directly measured by the polygraph, examiners may note xerostomia as a behavioural indicator of stress during the examination. Severe dry mouth may also indicate medication use that should be documented in the suitability screening.
Y
Yerkes-Dodson Inverted U Theory
The Yerkes-Dodson Inverted U (1908) models the relationship between arousal and performance as an inverted U-shape. Performance improves with arousal to an optimum, then declines. In PDD, under-aroused examinees (fatigue, medication) produce insufficient responses, while over-aroused examinees pr...
Yes Test Techniques
The Yes Test, attributed to John Reid, omits all comparison questions and directs the examinee to answer \"yes\" to all remaining questions. Preceded by special instructions designed to invite physical countermeasures from guilty examinees, it is used only when the examiner suspects countermeasure ...
Yes-No Technique Techniques
The Yes-No Technique, first reported by Richard Golden (1969), is similar to the Positive Control Technique. Each question is presented twice with the examinee instructed to answer truthfully once and deceptively once.
Yes/No Format Techniques
The standard question-and-answer format used in polygraph testing where all questions are constructed to require a simple "Yes" or "No" response. This format is mandatory in all APA-validated techniques because it standardises the examinee's verbal response, minimises cognitive interference from extended speech, and allows clean physiological measurement of the response to the question stimulus itself.
You Phase Techniques
The You Phase is the most commonly used format in the Backster Zone Comparison Technique. It addresses a single issue and single degree of involvement using two or three slightly different relevant questions plus a Sacrifice Relevant Question. It is considered powerful because of its tight focus ...
Z
A widely used variant of the Comparison Question Test developed by Cleve Backster. Divides the question sequence into "zones" where each relevant question is paired with a specific comparison question. The Federal Zone Comparison Test (FZCT) is the standard format used by most U.S. federal polygraph programs. APA-validated and considered one of the most reliable diagnostic polygraph testing techniques.
A grouping of questions within a Zone Comparison Test that share the same functional role. Backster defined three zones: Red Zone (relevant questions), Green Zone (comparison questions), and Black Zone (symptomatic questions). Each zone is designed to activate a different psychological concern. The zone structure enables paired scoring by matching specific relevant questions against specific comparison questions.
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