What psychologists should know about lie detection

This 1987 chapter by Iacono and Patrick provided psychologists with a comprehensive critical review of polygraph testing techniques, examining the scientific evidence for the Control Question Test (CQT) and Guilty Knowledge Test (GKT). The authors found that CQT validity studies produced mixed results with potential bias against the innocent, while the GKT showed laboratory promise but remained rarely used in practice.

This was a comprehensive critical literature review examining field studies using confession-verified cases and laboratory analog studies, systematically evaluating the validity research and theoretical foundations of major polygraph techniques including the CQT, GKT, and Relevant-Irrelevant tests.

This landmark 1987 chapter provided a 30-page critical synthesis of polygraph science for forensic psychologists at a crucial juncture before the 1988 Employee Polygraph Protection Act. Iacono and Patrick systematically reviewed validity research across three major polygraph techniques, identifying methodological strengths and weaknesses in both field and laboratory paradigms. The authors documented that the CQT lacked sound scientific foundation and rested on implausible psychological assumptions, while the more theoretically sound GKT remained largely unused in practice despite laboratory promise. By exposing the weak empirical basis of widely-used techniques, the work significantly influenced both scientific discourse and legal admissibility debates.

This foundational review provided essential knowledge to psychologists about a widely-used but scientifically contested forensic tool, directly influencing court admissibility determinations and policy debates around workplace testing. The work established critical standards for evaluating polygraph validity research and became the foundation for decades of subsequent scientific scholarship on deception detection.

Background & Context

This 1987 chapter by William G. Iacono and Christopher J. Patrick represented a 30-page comprehensive review that introduced psychologists to the scientific foundations—and limitations—of polygraph testing at a critical juncture in the field's history. Published in the first edition of the Handbook of Forensic Psychology, the work arrived during intense debate about polygraph validity and just five years before the 1988 Employee Polygraph Protection Act would restrict private-sector testing.

The chapter emerged from the broader scientific scrutiny inspired by David Lykken's work, filling a crucial educational gap for forensic practitioners. It described the most common polygraph techniques, reviewed research on their accuracy, and discussed typical applications, providing psychologists with essential knowledge about a widely-used but scientifically contested forensic tool.

Research Design & Methodology

This was a comprehensive critical review and synthesis rather than an empirical study. The authors systematically examined the scientific literature on polygraph testing, organizing their analysis around the major testing techniques used in the field.

The methodology involved critical evaluation of existing validity research across multiple dimensions:

• Field studies using real criminal cases with confession-verified ground truth
• Laboratory analog studies with mock crimes and known guilty/innocent participants
• Comparison of testing techniques: Control Question Test (CQT), Guilty Knowledge Test (GKT), and Relevant-Irrelevant tests
• Analysis of theoretical foundations underlying each polygraph methodology

The authors provided detailed critiques of field studies that used confessions to determine ground truth, identifying fundamental methodological problems that would become central to ongoing scientific debates about polygraph validity.

Results & Key Findings

The review found that field and laboratory studies on the validity of CQT results had produced mixed results: some studies found the CQT accurate with both guilty and innocent subjects, while others found it quite fallible and strongly biased against the innocent. This became a foundational observation cited extensively in subsequent polygraph literature.

Key findings included:

• The Control Question Test (CQT) was the most commonly used technique in specific incident investigations; the Guilty Knowledge Test (GKT) required subjects to respond to crime details posed in multiple-choice format
• Although the GKT had been found accurate in laboratory studies, no field research had been done and it was rarely used in practice
• The main advantage of laboratory studies—certainty of ground truth—was the major disadvantage of field studies, which typically established ground truth using confessions
• Theoretical concerns: The CQT lacked a sound scientific foundation and rested on implausible psychological assumptions

Discussion & Significance

This chapter became one of the most influential critical reviews of polygraph testing, establishing Iacono and Patrick as leading scientific voices on deception detection. Beginning in 1987, Iacono and Patrick published and periodically updated reviews of the three major polygraph techniques for forensic psychology, with this chapter serving as the foundation for decades of subsequent scholarship.

The work's significance extended beyond academia into legal and policy realms. By systematically documenting the weak scientific basis of the CQT and the unrealized potential of the GKT, the authors provided ammunition for courts considering polygraph admissibility and policymakers evaluating workplace testing. The authors concluded it was not possible to use existing literature to accurately estimate CQT validity due to fundamental methodological limitations.

The chapter also highlighted a persistent paradox: despite laboratory evidence supporting the GKT and its potential to provide safeguards for the innocent, it remained rarely used in the field, while the scientifically questionable CQT dominated practice.

Limitations & Considerations

As a literature review, this work was limited by the quality and scope of available primary research at the time. Laboratory mock crime studies were recognized as too unlike real life to offer realistic insight, with trivial consequences for failing and guilty individuals tested immediately after simulated crimes. Conversely, field studies suffered from the inability to establish truly independent ground truth.

The chapter necessarily reflected the state of knowledge in 1987, before developments in neuroimaging, computerized scoring algorithms, and more sophisticated statistical methods. The limited field data on the GKT meant the authors could not fully evaluate its real-world performance despite its theoretical promise.

Practical Applications

This chapter served as essential reading for psychologists entering forensic practice, providing the scientific literacy needed to evaluate polygraph evidence critically. For practitioners serving as expert witnesses, the work offered a scientifically grounded framework for testifying about polygraph limitations. For attorneys, it provided authoritative ammunition for challenging polygraph admissibility in court.

The review's practical impact extended to policy: by documenting the scientific community's concerns about CQT validity and the superior theoretical foundation of the GKT, it supported arguments for reforming polygraph practice and restricting reliance on scientifically dubious techniques in high-stakes decisions about employment, criminal justice, and security clearances.