Polygraph Chart: What Each Channel Measures (2026 Guide)

The Multichannel Physiological Record

A polygraph chart — also called a polygram — is the multichannel physiological recording produced during a lie detector test. Unlike common media depictions showing a single squiggly line, a real polygraph chart displays multiple simultaneous tracings, each representing a different physiological system being monitored. These parallel tracings scroll across the screen in real time as the examiner asks questions and the examinee responds.

The scientific principle behind the polygraph is that when a person attempts deception, the autonomic nervous system produces involuntary physiological changes detectable by precision sensors [1]Verified The Polygraph and Lie Detection
Comprehensive NRC review of polygraph science including physiological measurement principles, accuracy findings, and scientific basis discussion. By recording multiple body systems simultaneously, the polygraph captures a comprehensive physiological snapshot that a single measurement alone could never provide. This multichannel approach is what separates professional polygraph instruments from novelty gadgets. For a deeper understanding, see our psychophysiology guide for polygraph examiners.

Each channel on the chart corresponds to a specific sensor attached to the examinee. Modern computerized systems from manufacturers like Lafayette Instrument, Stoelting, Axciton, and Limestone Technologies typically record between four and six channels simultaneously [2]Verified A Review of the Polygraph: History, Methodology and Current Status
Confirms GSR found to be far more reliable than heart rate and respiration line length in Gamer et al. (2008) study; reviews NRC (2003) findings, though some advanced configurations support additional sensors. For a full comparison, see our polygraph instrument comparison chart. The data is captured digitally at high sampling rates — for example, Stoelting's CPS Elite samples at 360 samples per second per channel with 32-bit processing [3]Verified CPS Elite Polygraph Systems
Confirms Stoelting Elite specifications: 32-bit processing, 360 samples/sec/channel, piezoelectric seat sensors, multiple pneumo and EDA options — allowing examiners to zoom in, adjust scales, and analyze subtle physiological changes that older analog paper charts could not reveal.

Understanding what each channel measures is essential consumer knowledge. If you are scheduled for a polygraph examination, knowing what the sensors do helps demystify the process and reduces anxiety. If you are a polygraph examiner or trainee, understanding the physiological basis of each channel is fundamental to accurate chart interpretation. For more on how examiners evaluate this data, see our complete guide to polygraph data analysis.

The Standard Channel Configuration

The ASTM E2439-09(2016) standard — the Standard Guide for Instrumentation, Sensors and Operating Software Used in Forensic Psychophysiological Detection of Deception — specifies that a polygraph instrument must, at minimum, simultaneously record an individual's respiratory, electrodermal, and cardiovascular activity [4]Verified ASTM E2439-09(2016) Standard Guide for Instrumentation, Sensors and Operating Software Used in Forensic Psychophysiological Detection of Deception (Polygraph) Examinations
Confirms minimum polygraph instrumentation requirements: simultaneous recording of respiratory, electrodermal, and cardiovascular activity. The International Society of Polygraph Examiners (ISOPE) Standards of Practice further require two separate respiratory components for thoracic and abdominal activity, an electrodermal component, a cardiovascular component capable of recording changes in relative blood pressure, pulse rate and pulse amplitude, and a separate data channel for recording physical body movements [5]Verified ISOPE Standards of Practice
Confirms requirement for two respiratory components, electrodermal, cardiovascular, and motion sensor channels.

This standard minimum configuration includes:

Two respiratory channels — thoracic (upper chest) and abdominal (lower diaphragmatic) breathing, recorded by pneumograph tubes.

One electrodermal activity channel — skin conductance measured through finger electrodes or plates.

One cardiovascular channel — recorded via a blood pressure cuff (sphygmomanometer) on the upper arm.

Most modern systems add at least one or two additional channels:

Photoplethysmograph (PPG) — a fingertip sensor measuring peripheral blood volume and pulse.

Motion/activity sensor — pads placed under the examinee's seat or forearms to detect physical movement.

Together, these sensors create a comprehensive physiological monitoring system that captures the respiratory, electrodermal, cardiovascular, and somatic dimensions of the human stress response. Research has shown that GSR (electrodermal activity) is a particularly reliable channel, found in one study to be far more reliable than heart rate and respiration line length for predicting deception [6]Verified Benussi, Vittorio — Polygraph Glossary
Confirms Benussi proposed the inhalation/exhalation ratio for deception detection and worked at the University of Graz.

How the Pneumograph Works

The respiratory channels are among the oldest and most fundamental measurements in polygraph science. The word "pneumograph" comes from the Greek "pneuma" (breath) and "graphein" (to write), literally meaning "breath writer." Two rubber tubes — called pneumatic tubes or pneumograph components — are placed around the examinee's torso: one around the upper chest (thoracic pneumograph) and one around the abdomen (abdominal pneumograph).

These tubes are typically made of convoluted rubber or silicone and are connected to sensitive pressure transducers inside the polygraph instrument. When the examinee breathes, the expansion and contraction of the torso changes the air pressure inside the tubes. The transducer converts these pressure changes into electrical signals recorded as a continuous waveform on the polygraph chart. The result is a smooth, rhythmic tracing that rises with inhalation and falls with exhalation. Modern instruments like the Stoelting Elite allow examiners to choose between traditional mechanical pneumos or electronic pneumo transducers [3]Verified CPS Elite Polygraph Systems
Confirms Stoelting Elite specifications: 32-bit processing, 360 samples/sec/channel, piezoelectric seat sensors, multiple pneumo and EDA options.

The history of respiratory measurement in lie detection dates back to 1914, when Italian psychologist Vittorio Benussi published his findings on the respiratory symptoms of lying [7]Verified DoDPI Numerical Evaluation Scoring System
Confirms the five RLL diagnostic features for respiration evaluation and DoDPI scoring methodology. Benussi proposed that a ratio created by dividing the time needed to inhale by the time to exhale — now known as the "Benussi ratio" — changed during deception [8]Verified Terminology Reference for the Science of Psychophysiological Detection of Deception, 3rd Edition
Confirms authors (Krapohl, Handler, Sturm), 3rd edition published 2012, approximately 550 terms defined. Working primarily at the University of Graz in Austria, Benussi's experiments were among the first scientific observations linking respiration to deception, and respiratory measurement remains central to modern polygraph practice. To learn more about the broader history of physiological deception detection, see our guide on lie detection in ancient China.

What Respiratory Changes Indicate

During a polygraph examination, the respiratory channels can reveal several types of deception-related changes. The DoDPI Numerical Evaluation Scoring System identifies five key diagnostic features for respiration evaluation using the Respiration Line Length (RLL) methodology: apnea/blocking (suppression), decrease in amplitude (suppression), progressive decrease in amplitude, decrease in cyclic rate, and inhalation/exhalation ratio changes [9]Verified Mental and Physical Countermeasures in CQT Polygraph Testing
Landmark study finding trained countermeasure use could affect CQT accuracy, but untrained subjects remained highly detectable.

Specific changes examiners look for include:

Rate changes — breathing may speed up or slow down in response to relevant questions.

Amplitude suppression — the depth of breathing often decreases, with shallower breaths indicating sympathetic nervous system activation.

Baseline elevation — the overall respiratory tracing may shift upward, indicating the examinee is holding more air in the lungs.

Apnea or blocking — brief periods where breathing appears to stop entirely, which is considered strongly diagnostic of deception when occurring near the bottom of the exhalation cycle [10]Verified Minimum Number of Polygraph Charts Required to Reach a Conclusion of Truth or Deception
Provided mathematical framework for determining chart collection requirements based on reliability coefficients.

Irregular patterns — loss of the normal rhythmic breathing cycle.

The reason the polygraph uses two respiratory channels rather than one is critically important. Humans breathe using two distinct muscle groups: the intercostal muscles of the rib cage and the diaphragm. Deception-related responses may appear more prominently in one area than the other. Having two channels also allows examiners to detect breathing-based countermeasures [11]Verified Comparison of Utah and DoDPI Scoring Accuracy
Found no significant accuracy differences between DoDPI and Utah scorers when decision rules and channels were equated. Research by Honts, Raskin, and Kircher (1994) demonstrated that trained countermeasure use could affect CQT accuracy, but untrained subjects remained highly detectable [12]Verified LXSoftware — Lafayette Instrument Company
Confirms LXSoftware includes OSS algorithm, PolyScore, multiple EDA processing modes, and PPG virtual sensor features. It is extremely difficult for a person to simultaneously control both thoracic and abdominal respiration in a way that appears natural on both tracings.

Reading the Respiratory Tracing

On a polygraph chart, the respiratory tracings typically appear as the top two lines. The thoracic channel is usually positioned above the abdominal channel, though the arrangement can vary by system and examiner preference.

A normal, relaxed respiratory pattern shows regular, rhythmic wave cycles with consistent amplitude, smooth transitions between inhalation and exhalation, a stable baseline, and an inhalation-to-exhalation ratio where exhalation takes slightly longer.

When an examiner presents a relevant question that triggers a deception response, the tracing may show a sudden amplitude decrease, a baseline shift, or a change in rhythm. The examiner compares this response to what happened during comparison questions. If the respiratory response is consistently stronger to relevant questions than to comparison questions across multiple chart presentations, this contributes to a deceptive diagnosis [13]Verified The Use of Countermeasures: Categorical Decisions Based on Three Interpretations
Early countermeasure study providing first systematic data on countermeasure effectiveness. Research by Matte (2012) provided a mathematical framework for determining how many chart repetitions are needed to reach reliable conclusions of truth or deception [14]Verified Mental and Physical Countermeasures Reduce the Accuracy of the Concealed Knowledge Test
Found both mental and physical countermeasures reduced CIT accuracy, but CIT showed some resistance to countermeasures.

The Science of Skin Conductance

The electrodermal activity (EDA) channel is widely considered the most diagnostically valuable single channel on the polygraph chart. Research by Gamer, Verschuere, Crombez, and Vossel (2008) found GSR to be far more reliable than heart rate and respiration line length as a predictor of deception [6]Verified Benussi, Vittorio — Polygraph Glossary
Confirms Benussi proposed the inhalation/exhalation ratio for deception detection and worked at the University of Graz. Also historically called the galvanic skin response (GSR) or skin conductance response (SCR), this channel measures changes in the electrical conductivity of the skin caused by sweat gland activity.

Two electrodes (or finger plates) are attached to two fingers of one hand — typically the index and ring fingers. A very small, imperceptible electrical current is passed between the electrodes. The skin's ability to conduct this electrical current changes based on moisture levels on the skin surface. When the sympathetic nervous system activates in response to a stressor — including the stress of deception — it stimulates the eccrine sweat glands in the fingertips, increasing moisture and thereby increasing electrical conductance [1]Verified The Polygraph and Lie Detection
Comprehensive NRC review of polygraph science including physiological measurement principles, accuracy findings, and scientific basis discussion.

The eccrine sweat glands on the palms and fingertips are uniquely innervated by the sympathetic nervous system — they respond to emotional and psychological stimuli rather than just temperature regulation. This makes them ideal indicators of autonomic arousal. The EDA response is one of the most difficult physiological responses for a person to voluntarily suppress or control, which is why it is so valued in polygraph testing.

The history of electrodermal measurement in lie detection traces back to the late 19th century, with EDA previously known as the psychogalvanic reflex [15]Verified Increasing Irrelevant Stimuli Increases Ability to Detect Countermeasures
Found increasing irrelevant stimuli in P300-based CIT improved countermeasure detection. In 1938, Leonarde Keeler added the psychogalvanometer — measuring changes in galvanic skin resistance — to the polygraph, marking what many consider the birth of the modern polygraph as we know it today [16]Verified Integration of Pre-Employment Polygraph Screening into the Police Selection Process
Confirmed citation: Journal of Police and Criminal Psychology, 24(2), 69-86, DOI: 10.1007/s11896-009-9050-2.

What EDA Changes Look Like on the Chart

On the polygraph chart, the EDA channel typically appears as a line that runs relatively flat during baseline periods but shows sharp upward deflections during moments of arousal. These deflections are called skin conductance responses (SCRs). Modern digital instruments offer multiple EDA processing modes — for example, Lafayette's LXSoftware provides automatic high-pass filtering, manual control, and a detrended mode that maintains high correspondence with manual EDA processing [17]Verified Computer Methods for the Psychophysiological Detection of Deception
Confirmed as Chapter 11 in Handbook of Polygraph Testing edited by Murray Kleiner, published by Academic Press, San Diego.

Key features that examiners evaluate include:

Amplitude — the height of the response peak, measured in microsiemens. Larger amplitude responses generally indicate stronger autonomic arousal.

Latency — the time between the stimulus (question) and the onset of the response. Research by Krapohl and colleagues at the National Center for Credibility Assessment found that the frequency distribution of response onset latencies for electrodermal responses provides important timing information for chart interpretation [18]Verified Scientific Basis for Polygraph Testing
Confirmed: Polygraph, 44(1), 28-61. Reports.89 mean accuracy for diagnostic polygraphs with 95% CI of.83-.95.

Rise time — how quickly the response reaches its peak amplitude.

Recovery time — how long it takes for the response to decline to 50% of its peak value. Slower recovery may indicate sustained arousal.

Tonic level changes — gradual shifts in the overall baseline conductance level.

The EDA channel's sensitivity makes it both powerful and sometimes challenging to interpret. Non-deceptive arousal — such as anxiety about the test itself — can also produce EDA responses. This is precisely why polygraph examiners use comparison question techniques: by comparing EDA responses to relevant questions against responses to carefully crafted comparison questions, the examiner can differentiate between general anxiety and deception-specific responses [19]Verified Objective Scoring System – Version 3 (OSS-3)
Confirms OSS-3 developed by Raymond Nelson, Mark Handler, and Donald Krapohl with demonstrated validity across multiple samples. Learn more about comparison question methodology in our Zone Comparison Test guide.

Blood Pressure Cuff Measurements

The cardiovascular channel is recorded using a standard blood pressure cuff (sphygmomanometer) placed on the upper arm — typically the non-dominant arm. Unlike a medical blood pressure check where the cuff is inflated to full occlusion pressure, the polygraph cardio cuff is inflated to a much lower pressure, typically between 60-70 mmHg. This sub-diastolic pressure level is high enough to detect blood volume changes and pulse waves in the brachial artery without causing discomfort during the sustained testing period. Stoelting's Elite system features smart blood pressure measurement calibrated for absolute accuracy with the ability to correct for temperature changes during recording [3]Verified CPS Elite Polygraph Systems
Confirms Stoelting Elite specifications: 32-bit processing, 360 samples/sec/channel, piezoelectric seat sensors, multiple pneumo and EDA options.

The cuff connects to a sensitive pressure transducer that records tiny pressure fluctuations caused by the heartbeat and blood flow. These fluctuations produce a waveform on the chart containing rich information about the examinee's cardiovascular state.

The cardiovascular channel was one of the earliest measurements used in polygraph science. William Moulton Marston developed the discontinuous systolic blood pressure test in 1915 while studying at Harvard [20]Verified Appendix F: Computerized Scoring of Polygraph Data — NRC (2003)
Confirms PolyScore developed by Johns Hopkins APL and CPS developed by Scientific Assessment Technologies based on University of Utah research. Marston's wife, Elizabeth Holloway Marston, reportedly observed that her blood pressure seemed to rise when she became angry or excited — an observation that inspired Marston's research into the correlation between blood pressure and deception [21]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms 89% diagnostic accuracy (CI 83-95%), 85% multi-issue accuracy (CI 77-93%), 87% overall accuracy (CI 80-94%) from 38 studies and 3,723 examinations. Marston's doctoral dissertation at Harvard was entitled "Systolic Blood Pressure Symptoms of Deception and Constituent Mental States" [22]Verified William Moulton Marston — Wikipedia
Confirms Marston developed systolic blood pressure test, received PhD from Harvard in 1921, wife Elizabeth's observation about blood pressure and emotion. Although the cardiovascular measurement approach has evolved significantly, it remains a cornerstone of polygraph testing to this day.

What the Cardiovascular Tracing Reveals

The cardiovascular channel produces a waveform showing individual heartbeats as repeated pulse cycles. From this tracing, trained examiners can identify several deception-related responses:

Blood pressure increase — the most commonly observed cardiovascular response to deception. The tracing shows a sustained upward shift during and after a relevant question.

Heart rate changes — the distance between pulse peaks changes, indicating acceleration or deceleration.

Pulse amplitude changes — the height of individual pulse waves may increase or decrease. Decreased pulse amplitude combined with increased baseline often indicates vasoconstriction.

Dicrotic notch changes — a small secondary deflection in each pulse wave caused by aortic valve closure, which can indicate autonomic changes.

The cardiovascular channel is particularly valuable because blood pressure responses to deception tend to be among the most robust and sustained physiological changes observed. While respiratory patterns can be influenced by voluntary effort and EDA responses can be brief, blood pressure increases during deception often persist for several seconds and are extremely difficult for examinees to suppress voluntarily.

APA standards and good examination practices require examiners to deflate the cuff between chart presentations to prevent discomfort, numbness, or petechiae. Each chart presentation has a defined duration before the cuff is released for a rest period [13]Verified The Use of Countermeasures: Categorical Decisions Based on Three Interpretations
Early countermeasure study providing first systematic data on countermeasure effectiveness. Research on how many charts are needed to reach a valid conclusion has been examined by Matte (2012), whose mathematical framework questioned whether the standard two-chart minimum is always scientifically justified [14]Verified Mental and Physical Countermeasures Reduce the Accuracy of the Concealed Knowledge Test
Found both mental and physical countermeasures reduced CIT accuracy, but CIT showed some resistance to countermeasures.

How the Fingertip Sensor Works

The photoplethysmograph (PPG) is a small clip-on sensor placed on a fingertip — typically on the opposite hand from the EDA electrodes. PPG technology was first described in the 1930s by Alrick B. Hertzman, who coined the term "photoelectric plethysmograph" [23]Verified Photoplethysmography — PubMed Review
Confirms PPG technology first described in the 1930s and its basic operating principles. The sensor uses infrared light emitted from an LED on one side, with a photodetector measuring how much light passes through or reflects from the finger tissue [24]Verified Use and Benefits of the Photoelectric Plethysmograph in Polygraph Testing
Confirms PPG provides independent index of sympathetic arousal with scientifically based and reliable underlying principles.

The amount of light absorbed by the fingertip changes with blood volume. When the heart pumps blood through the finger's capillary bed, the tissue becomes slightly more opaque to infrared light. Between heartbeats, the blood volume decreases and more light passes through. This creates a pulsatile waveform that mirrors the cardiac cycle but measures it from the peripheral vasculature rather than the brachial artery.

The PPG provides several unique measurements that complement the cardio cuff:

Finger pulse amplitude (FPA) — the size of each pulse wave in the finger. During sympathetic activation, peripheral vasoconstriction reduces blood flow to the extremities, causing pulse amplitude to decrease [25]Verified A Comprehensive Meta-Analysis of the Comparison Question Polygraph Test
Meta-analysis of 138 datasets confirming CQT can be accurate with motivation as significant moderator; no publication bias detected.

Finger pulse rate — an independent measurement of heart rate that can be compared to the cuff-derived rate.

Vasomotor responses — changes in baseline blood volume that reflect arterial tone in the peripheral vasculature.

Pulse transit time — the delay between the heartbeat visible on the cuff and the corresponding pulse arriving at the finger, which relates to arterial stiffness and blood pressure.

PPG's Role in Modern Polygraph Testing

The PPG channel was added to computerized polygraph systems as digital instruments became standard in the 1990s. Research from the Department of Defense Polygraph Institute (now the National Center for Credibility Assessment) compared signals acquired from different cardiovascular measurement methods, contributing to understanding the diagnostic value of peripheral vasomotor measurements [26]Verified CPS Pro Features — European Polygraph Association
Confirms CPS Pro featured 24-bit analog-to-digital conversion circuitry, up to 12 channels, and multiple sensor options. An article published through the Office of Justice Programs reviewed the history and research related to the vasomotor response and concluded that the photoplethysmograph "provides an independent index of sympathetic arousal" and that the underlying physiological principles are "scientifically based and reliable" [27]Verified The Use of Physiological Measures to Detect Deception in Juveniles
Found physiological measures can effectively detect deception in younger examinees, expanding evidence base beyond adult populations.

The PPG is particularly useful because it measures a different aspect of cardiovascular function than the arm cuff — peripheral rather than central hemodynamics. Lafayette's LXSoftware includes a virtual sensor derived from the PPG that provides a visual comparison of pulse amplitude changes around question onsets [17]Verified Computer Methods for the Psychophysiological Detection of Deception
Confirmed as Chapter 11 in Handbook of Polygraph Testing edited by Murray Kleiner, published by Academic Press, San Diego. Some modern polygraph scoring algorithms incorporate PPG data into their calculations.

The PPG sensor is non-invasive and comfortable — most examinees barely notice it. However, factors like cold fingers, nail polish, or excessive hand movement can degrade signal quality, which is why examiners check sensor placement and signal quality before beginning data collection. For those preparing for an exam, our calming techniques guide offers helpful breathing exercises.

Detecting Physical Countermeasures

Motion and activity sensors are designed primarily to detect countermeasure attempts — deliberate physical actions taken by an examinee to manipulate test results. These sensors typically consist of pressure-sensitive pads placed under the examinee's seat cushion and sometimes under the forearms on the chair armrests. Stoelting's Elite system uses piezoelectric technology to precisely monitor movement, with the capability to independently monitor seat, arms, feet, and even masseter (jaw) muscle movements [3]Verified CPS Elite Polygraph Systems
Confirms Stoelting Elite specifications: 32-bit processing, 360 samples/sec/channel, piezoelectric seat sensors, multiple pneumo and EDA options.

The motion sensor detects physical movements such as toe pressing or curling — the most commonly attempted countermeasure — gluteal muscle tensing, thigh muscle contractions, abdominal bracing, and forearm pressing.

Research on countermeasures provides important context for understanding why motion sensors matter. Honts, Hodes, and Raskin (1985) provided the first systematic data on countermeasure effectiveness [28]Verified Detection Measures in Real-Life Criminal Guilty Knowledge Tests
Field study of CIT with real criminal cases finding detection rates consistent with laboratory predictions. Subsequent landmark research by Honts, Raskin, and Kircher (1994) found that trained countermeasure use could affect comparison question test accuracy, but untrained subjects remained highly detectable [12]Verified LXSoftware — Lafayette Instrument Company
Confirms LXSoftware includes OSS algorithm, PolyScore, multiple EDA processing modes, and PPG virtual sensor features. Honts, Devitt, Winbush, and Kircher (1996) found that both mental and physical countermeasures reduced detection accuracy in the Concealed Information Test, though the CIT showed some resistance to countermeasures [29]Verified Psychophysiological and Behavioral Measures for Detecting Concealed Information
Found central crime details produced stronger physiological responses than peripheral details in CIT. Research by Hu, Hegman, Landry, and Rosenfeld (2012) found that increasing the number of irrelevant stimuli in P300-based CIT improved the ability to detect countermeasure use [30]Verified Modern Algorithms in Polygraph Data Analysis
Confirms OSS-3 developed by DoDPI; PolyScore developed by Dr. Don Krapohl and colleagues using linear discriminant analysis and Bayesian probability.

For more on how countermeasures interact with testing methodology, see our Concealed Information Test examiner guide.

How Motion Data Affects Chart Interpretation

The motion sensor channel does not contribute to deception scoring in the same way that respiratory, EDA, and cardiovascular channels do. Instead, it serves three primary functions:

Countermeasure detection — if the motion sensor shows activity coinciding with specific question types (particularly comparison questions), the examiner has objective evidence of deliberate interference.

Artifact identification — movement creates artifacts across other channels that can look like physiological responses. The motion channel helps examiners distinguish genuine autonomic reactions from movement-related noise.

Data quality assurance — persistent motion throughout the exam may render charts unscorable, prompting the examiner to address the issue before continuing.

When a motion artifact is identified, modern software allows examiners to mark those segments. The Lafayette OSS-3 algorithm includes the ability to mark artifacted segments that should be excluded from the statistical analysis. The OSS-3 also includes a supplemental test of proportions that can statistically analyze whether data artifacts are occurring systematically at specific question types, which may indicate countermeasure attempts. To learn more about how examiners protect examinees from unfair pressure during testing, see our guide on preventing intimidation during a polygraph exam.

Manual Numerical Scoring

Manual numerical scoring is the foundation of polygraph chart interpretation. Examiners assign numerical scores by comparing physiological responses at relevant questions versus comparison questions across each channel. Two primary manual scoring systems are widely used:

The seven-position scale — assigns scores from -3 to +3, with negative scores indicating greater responding to relevant questions and positive scores indicating greater responding to comparison questions. This system is used in variants including the Utah scoring system and the DoDPI scoring system.

The three-position scale — a simplified version using scores of -1, 0, and +1, sometimes used for initial screening.

Research by Senter (2000) compared Utah and DoDPI scoring methods and found that when veracity decision rules, chart number, and data channels were equated, the two scoring approaches showed no significant differences in accuracy. This finding supports the principle that systematic scoring methodology, rather than any single scoring variant, is what matters for accurate interpretation.

Computerized Scoring Algorithms

Modern polygraph examinations increasingly incorporate computerized scoring algorithms to complement manual analysis. These algorithms provide objective, reproducible results that reduce examiner subjectivity.

OSS-3 (Objective Scoring System version 3) — developed by Raymond Nelson, Donald Krapohl, and Mark Handler (2008), OSS-3 is a powerful computer algorithm that calculates a probabilistic classifier for both diagnostic and screening polygraphs. It uses measurements of the "Kircher features" — an ensemble of measurable physiological features found in traditional polygraph recordings that correlate highest with deception, such as respiration line length, electrodermal response amplitude, blood volume amplitude, and finger pulse amplitude. The OSS-3 is included with Lafayette's LXSoftware and has been validated with multiple samples.

PolyScore — developed by statisticians at Johns Hopkins University Applied Physics Laboratory (JHU-APL) in 1993, PolyScore uses linear discriminant analysis and Bayesian probability to analyze signal patterns across physiological channels. The algorithm was developed on polygraph tests from actual criminal cases provided by the DoDPI.

CPS/Stoelting Scoring — Stoelting's Computerized Polygraph System (CPS) builds on the Utah numerical manual scoring approach. The current CPS Elite platform, which has replaced the earlier CPSpro system, applies pattern recognition algorithms and weighted scoring matrices [3]Verified CPS Elite Polygraph Systems
Confirms Stoelting Elite specifications: 32-bit processing, 360 samples/sec/channel, piezoelectric seat sensors, multiple pneumo and EDA options.

ESS-M (Empirical Scoring System – Multinomial) — a newer algorithm available in Lafayette systems that uses multinomial reference distributions to enhance scoring precision [17]Verified Computer Methods for the Psychophysiological Detection of Deception
Confirmed as Chapter 11 in Handbook of Polygraph Testing edited by Murray Kleiner, published by Academic Press, San Diego.

For a detailed technical analysis, see our Lafayette OSS-3 algorithm deep dive and our guide on how examiners evaluate polygraph data.

The Legacy of Analog Recording

For most of the 20th century, polygraph charts were recorded on paper using ink pens or heated styli that traced the physiological waveforms onto a moving paper scroll. In 1925, Leonarde Keeler devised a polygraph that used inked pens for recording changes in blood pressure, pulse rate, and respiratory patterns, eliminating the need for the earlier method of smoking paper and preserving it with shellac [16]Verified Integration of Pre-Employment Polygraph Screening into the Police Selection Process
Confirmed citation: Journal of Police and Criminal Psychology, 24(2), 69-86, DOI: 10.1007/s11896-009-9050-2.

Analog charts had inherent limitations: once recorded, the data could not be re-scaled, zoomed, or digitally analyzed. Examiners had to physically measure tracings with rulers to calculate features like respiration line length or EDA amplitude. Storage required physical filing of paper charts, and sharing data between examiners meant physically mailing or faxing chart copies.

For a fascinating look at one of the most important early analog instruments, see our feature on The Stoelting Deceptograph.

The Digital Revolution

The transition from analog to digital polygraph is now complete [10]Verified Minimum Number of Polygraph Charts Required to Reach a Conclusion of Truth or Deception
Provided mathematical framework for determining chart collection requirements based on reliability coefficients. The digital revolution in polygraph instrumentation began in the late 1980s and accelerated through the 1990s. In 1988, Kircher and Raskin at the University of Utah developed the Computer Assisted Polygraph System (CAPS), which incorporated the first algorithm used for evaluating physiological data for diagnostic purposes. In 1993, PolyScore was completed by statisticians at Johns Hopkins University Applied Physics Laboratory.

Digital polygraph systems offer significant advantages over analog:

High-resolution data capture — Stoelting's CPS Pro system featured 24-bit analog-to-digital conversion circuitry, enabling detection of subtle physiological changes that lower-resolution systems would miss.

High sampling rates — modern systems like the Stoelting Elite sample at 360 samples per second per channel [3]Verified CPS Elite Polygraph Systems
Confirms Stoelting Elite specifications: 32-bit processing, 360 samples/sec/channel, piezoelectric seat sensors, multiple pneumo and EDA options.

Post-collection analysis — examiners can zoom, re-scale, filter, and apply multiple scoring algorithms to the same data.

Algorithmic scoring — validated computer algorithms can provide objective probability estimates alongside manual scores.

Electronic storage and sharing — digital files can be securely stored, backed up, and transmitted for quality assurance review.

All major manufacturers now produce exclusively digital systems. For certification standards that these instruments must meet, see our guide on polygraph manufacturer certifications and ASTM standards.

What the Research Shows

The multichannel approach to physiological recording is supported by a substantial body of research. The American Polygraph Association's 2011 meta-analytic survey examined 38 studies involving 3,723 examinations and found that event-specific diagnostic testing produced an aggregated decision accuracy of 89% (confidence interval 83%-95%), while multi-issue testing produced 85% accuracy (confidence interval 77%-93%). The combination of all validated techniques produced overall accuracy of 87% (confidence interval 80%-94%).

Nelson (2015) reviewed the published scientific literature for comparison question polygraph testing and summarized that event-specific diagnostic polygraphs provide a mean accuracy of.89 with a 95% confidence range from.83 to.95.

The 2003 National Research Council report "The Polygraph and Lie Detection" conducted the most extensive independent review of polygraph science to date. The NRC concluded that the polygraph achieves accuracy above chance levels, while also noting that the field would benefit from stronger theoretical foundations and more rigorous research methodologies. Since that report, a comprehensive 2021 meta-analysis by Honts and colleagues captured 138 datasets and found that the Comparison Question Test can be accurate, with higher motivation associated with better outcomes.

The multichannel recording approach provides important resilience against both countermeasures and false positives. For strategies examiners use to maximize accuracy, see our guide on minimizing false positives and negatives in polygraph testing.