Validity and reliability of the control question polygraph test: A scientific investigation

Background & Context

In the mid-1980s, polygraph testing faced mounting scientific scrutiny following David Lykken's influential critiques of the Control Question Test (CQT). Christopher Patrick and William Iacono entered this debate at a critical juncture, presenting their systematic investigation of CQT validity and reliability at the 1987 Society for Psychophysiological Research meeting and subsequently publishing comprehensive reviews that would shape academic discourse on polygraph testing for decades.

The Control Question Test represented the dominant polygraph format used in criminal investigations and forensic settings. The CQT, as the type of polygraph test most likely to be used in forensic settings, operated on theoretical assumptions that Patrick and Iacono would subject to rigorous examination. Their work addressed a fundamental gap: the lack of independent, methodologically sound validation of the CQT's claimed accuracy rates.

Research Design & Methodology

Patrick and Iacono's analysis focused on the implausible set of assumptions underlying the CQT, which they argued made it biased against innocent individuals and easy for guilty persons to defeat using countermeasures. Their investigation employed multiple methodological approaches to assess both the theoretical foundations and empirical performance of the CQT.

The researchers conducted systematic reviews of existing field and laboratory studies, with particular attention to methodological limitations. Field studies of real-life cases provided the best opportunity for estimating CQT error rates, but studies based on such cases were severely limited by methodological problems generally ignored by CQT proponents, as the main advantage of laboratory studies—certainty of ground truth—was the major disadvantage of field studies.

Key methodological considerations included:

• Ground truth establishment using confessions to identify the guilty and exculpate co-suspects
• Recognition that criterion information tends not to be independent of polygraph test outcomes
• Blind rescoring of polygraph charts to assess inter-rater reliability
• Analysis of sampling biases in field validation studies

Results & Key Findings

The researchers concluded that due to serious methodological problems characterizing research on CQT validity, it was not possible to use the existing literature to provide a satisfactory error rate estimate. This represented a fundamental challenge to polygraph proponents' accuracy claims.

Specific findings from Patrick and Iacono's broader research program revealed:

• Laboratory studies could not replicate the emotional characteristics of real-life polygraph examinations, while field studies were based on actual crimes but suffered from criterion contamination.
• Examiners often departed from strict chart-based decision making, with polygraph test opinions taking into account information besides chart data, including case facts from police reports, discussions with investigators, and subject behaviors during pre- and post-test interrogation.
• Scientists, including members of the Society for Psychophysiological Research and APA Fellows, held negative views about the CQT and did not believe it was based on sound theory, had adequate psychometric properties, or should be used as evidence in court.

The research documented that polygraph test scoring was highly reliable (e.g., interscorer reliability was .93 when 267 blindly rescored polygraph charts were compared to original police examiner scores). However, high scoring reliability did not translate to validity—examiners could consistently agree on incorrect decisions.

Discussion & Significance

Patrick and Iacono's work represented a watershed moment in polygraph science, establishing methodological standards that exposed fundamental flaws in CQT validation research. Their central thesis—that the CQT was based on implausible assumptions making it biased against the innocent and vulnerable to countermeasures—challenged the scientific legitimacy of the most widely used polygraph technique.

Beginning in 1987, Iacono and Patrick published and periodically updated comprehensive reviews of the three major polygraph techniques for forensic psychology and detection of malingering volumes, creating an enduring scholarly framework for critical evaluation. Their rigorous analysis influenced subsequent government reviews, including the National Research Council's 2003 comprehensive assessment.

The significance extended beyond academic circles. Their work contributed to persistent concerns that the comparison question test has a high false positive rate, though these scientific criticisms had little effect on polygraph practice or curtailed its use in government screening and sex offender management.

Limitations & Considerations

The analysis faced inherent constraints stemming from the nature of polygraph validation research itself. While field studies provided the best opportunity for estimating CQT error rates, they were severely limited by methodological problems, as ground truth establishment typically relied on confessions—creating the fundamental problem that this criterion was not independent of the polygraph test.

The review highlighted a paradox: laboratory studies could not replicate the emotional characteristics of real-life polygraph examinations, yet field studies suffered from criterion contamination and sampling biases. This methodological dilemma meant that it was not possible to use existing literature to provide satisfactory error rate estimates—a limitation of the research base itself rather than the authors' analysis.

Practical Applications

Patrick and Iacono's findings have profound implications for legal and forensic practice. Their conclusion that the CQT should not be used as evidence in court provided scientific ammunition for defense attorneys and influenced judicial decisions regarding polygraph admissibility. The research underscored that high examiner confidence and consistent scoring do not constitute scientific validity.

For practitioners and policymakers, this work demands recognition that polygraph opinions often incorporate extra-polygraphic sources of information including case facts, investigator discussions, and subject behaviors—suggesting the "test" functions more as an interrogation tool than an objective physiological measure. Consumers of polygraph services should understand that scientific consensus does not support the CQT's validity claims, despite its continued widespread use in government and criminal justice settings.