Admissibility of Polygraph Tests: The Application of Scientific Standards Post-Daubert

Application of behavioral science reliability and validity concepts to polygraph admissibility, arguing accuracy rates are unpredictable.

Scientific standards analysis examining reliability and validity evidence for polygraph.

Published in 1999 in Psychology, Public Policy, and Law, 5, 203–223, this work by Saxe and colleagues examined this topic area. Key findings include: Applied behavioral science concepts of reliability and validity to polygraph admissibility. Argued that accuracy rates are unpredictable and called for mutual language between scientists and courts. This work has direct implications for the legal treatment and admissibility of polygraph evidence.

The call for shared language between scientific and legal communities remains relevant for improving polygraph evidence presentation in court.

Background & Context

The 1999 Saxe and Ben-Shakhar paper emerged at a pivotal moment in the intersection of science and law. The U.S. Supreme Court's 1993 Daubert v. Merrell Dow Pharmaceuticals decision had modernized the long-standing Frye precedent and required courts to make scientific judgments, fundamentally altering how scientific evidence could be admitted in court. This shift placed unprecedented pressure on courts to evaluate the scientific validity of techniques like polygraph testing.

Courts, however, were not well-equipped to parse scientific arguments. Polygraph evidence had been controversial for decades, with jurisdictions split on its admissibility. The paper used this controversy as a case study to demonstrate both the challenges of applying Daubert and the communication gap between scientific and legal communities.

The timing was critical: polygraph testing was widely used in criminal justice, national security screening, and employment contexts, yet its scientific foundation remained hotly debated. The authors sought to apply rigorous psychometric standards to evaluate whether polygraph testing—specifically the Control Question Test (CQT)—could meet the Daubert criteria for admissibility.

Research Design & Methodology

This was a comprehensive theoretical and methodological analysis rather than an empirical study with participants. The authors discussed reliability and validity in relation to polygraph testing and the Daubert criteria, applying modern behavioral science concepts to evaluate existing polygraph research.

The methodological framework centered on applying Messick's (1995) unified theory of validity to polygraph testing. The analysis examined whether polygraph test results lack several components of construct validity, including substantive validity (theoretical), external validity, and convergent and discriminant validity. The authors systematically evaluated the polygraph literature against established psychometric standards.

Key analytical components included:

• Review of accuracy studies and their methodological quality
• Assessment of the CQT's theoretical foundations
• Application of the four Daubert criteria (testability, error rate, peer review, general acceptance)
• Examination of construct validity components using modern psychometric frameworks

Results & Key Findings

The central conclusion was that accuracy rates for polygraph testing are unpredictable and that none of the validity studies satisfy necessary methodological criteria. This finding directly challenged claims that polygraph testing had demonstrated sufficient scientific validity for court admissibility.

The validity analysis revealed critical deficiencies:

• No demonstrations establish an empirical relationship between CQT polygraph test's outcomes and other measures of the same construct (convergent validity)
• There are numerous demonstrations of the lack of discriminant validity, and the physiological changes monitored can reflect emotions unrelated to deception
• Even if examinees recall or think of some exciting or frightening event from their past, they might show the same response pattern

The paper demonstrated that the polygraph's physiological measurements lacked specificity to deception. The Control Question Test could not distinguish between anxiety about lying and anxiety from other sources, fundamentally undermining its theoretical basis.

This analysis points to the need for social scientists and courts to develop a mutually understood language to assess validity claims. The authors argued that legal terminology often conflated reliability with validity, creating confusion in evaluating scientific evidence.

Discussion & Significance

The paper's significance lies in its systematic application of modern psychometric standards to a forensic technique that had largely avoided such scrutiny. By demonstrating that the CQT lacks fundamental components of construct validity, Saxe and Ben-Shakhar provided a scientific framework for understanding why polygraph evidence should not meet Daubert standards.

This work influenced subsequent court decisions and scientific discourse about polygraph admissibility. In the United States, both the Frye and later Daubert decisions indicated that a chief obstacle to admissibility is the failure of the test to gain 'general acceptance' within the scientific community. The paper provided ammunition for judges skeptical of polygraph evidence by articulating specific scientific deficiencies rather than general concerns.

The authors' call for developing shared language between scientists and courts proved prescient. Their analysis highlighted that effective gatekeeping requires courts to understand not just whether a technique "works" in some general sense, but whether it possesses the specific components of validity necessary for its intended use. Courts must have the ability to weight scientific evidence and, although they need not become amateur scientists, they must become sophisticated consumers.

Limitations & Considerations

As a theoretical and review paper rather than an empirical study, the work's limitations relate to its scope and focus. The analysis concentrated primarily on the Control Question Test (CQT), the most commonly used polygraph technique, but devoted less attention to alternative approaches like the Guilty Knowledge Test (GKT), which some researchers argue has stronger theoretical foundations.

The paper's impact depends on courts' willingness and ability to engage with psychometric concepts like construct validity and discriminant validity. While the authors called for improved scientific literacy in the legal system, translating these concepts into judicial decision-making remains challenging. Additionally, the analysis was conducted within the American legal framework and may not fully translate to jurisdictions with different evidentiary standards.

Practical Applications

For legal practitioners and judges, this paper provides a roadmap for evaluating polygraph evidence under Daubert. It demonstrates that questions about polygraph admissibility cannot be answered simply by pointing to accuracy rates in published studies; courts must examine whether the underlying methodology satisfies fundamental scientific validity requirements. The analysis suggests that CQT polygraph evidence should generally fail Daubert challenges due to construct validity deficiencies.

For polygraph examiners and researchers, the paper issued a clear challenge: develop testing methods grounded in sound psychological theory with demonstrable construct validity, or accept that polygraph evidence will—and should—continue to face exclusion from court. The work underscored that improving polygraph's legal standing requires addressing fundamental theoretical problems, not merely conducting more accuracy studies with existing flawed methodologies. For consumers and those asked to take polygraph tests, the analysis provides scientific backing for skepticism about what such tests can actually prove about truthfulness.