The Empirical Basis for the Use of Directed Lie Comparison Questions in Diagnostic and Screening Polygraphs

Blalock, Nelson, Handler, and Shaw (2012) conducted a systematic review of the empirical literature examining directed lie comparison questions (DLCQs) in both diagnostic and screening polygraph formats. The review synthesized laboratory and field evidence to determine whether a scientific basis exists for the use of DLCQs as an alternative to the traditional probable lie comparison question (PLCQ). The authors concluded that DLCQs produce accuracy and effect sizes comparable to PLCQs while offering distinct advantages in standardization, ethical transparency, and ease of legal explanation.

Systematic narrative review synthesizing published laboratory analog studies, field validity research, and theoretical analyses comparing directed lie comparison questions (DLCQs) with probable lie comparison questions (PLCQs) across multiple polygraph formats and scoring systems.

This 2012 systematic review addressed a gap in polygraph literature by consolidating empirical evidence on directed lie comparison questions (DLCQs), which had been used operationally since the 1960s but lacked dedicated scientific review. The authors examined both diagnostic and screening polygraph formats, comparing DLCQ effectiveness against traditional probable lie comparison questions (PLCQs) through laboratory analog studies and field studies with verified ground truth. The review drew on landmark research including the Utah approach to the Comparison Question Test developed by Raskin and colleagues. The findings provided practitioners with research-grounded justification for using DLCQs, highlighting potential advantages in standardization, transparency, and ethical administration compared to PLCQs. The study concluded that sufficient empirical evidence existed to support DLCQs as scientifically defensible comparison stimuli.

The review provided scientific validation for the operational use of directed lie comparison questions, supporting their deployment in both diagnostic and screening polygraph contexts while highlighting advantages in standardization and ethical practice over traditional probable lie questions.

Background & Context

Since the Comparison Question Test (CQT) became the dominant polygraph framework in the mid-20th century, practitioners have debated the optimal construction of the comparison (control) question. Directed lie comparison questions (DLCQs) have been in use by some government agencies since the late 1960s, and have been described in polygraph research since at least 1981. Despite this long operational history, the scientific community had not produced a dedicated, consolidated evidence review specifically examining whether DLCQs were valid for use in both diagnostic and screening polygraph contexts.

There has been some question as to when it is advantageous or "permissible" to use directed lie comparison questions in polygraph testing — and, more specifically, whether it is scientifically valid to use DLCs in diagnostic and/or screening test formats. Blalock, Nelson, Handler, and Shaw (2012) published their review in APA Magazine to address this precise gap, consolidating the empirical record on DLCQs and providing practitioners with a research-grounded rationale for their deployment.

The timing was also significant from a theoretical standpoint. Competing schools of thought — particularly those championing the traditional Probable Lie Comparison Question (PLCQ) — had long held that PLCQs were superior because of their individualized, motivationally tailored construction. There may be some advantages to the DLCQ approach in terms of standardization, ease of use, transparency, ease of explanation in legal, judicial, scientific, and media contexts, as well as the ethics of their use and administration — advantages centered around the fact that DLCQs, unlike PLCQs, do not rely on psychological manipulation.

Research Design & Methodology

The 2012 paper by Blalock, Nelson, Handler, and Shaw is best characterized as a systematic narrative review synthesizing published laboratory experiments, field validity studies, and theoretical analyses bearing on the use of directed lie comparison questions. Rather than presenting new primary data, the authors evaluated the accumulated empirical literature to determine whether a sufficient evidence base existed to support DLCQs as scientifically defensible comparison stimuli.

Key design elements of the review included:

• Scope: Both diagnostic (single-issue criminal investigation) and screening (multi-issue security or employment) polygraph formats were examined separately
• Comparison framework: Effect sizes and accuracy rates for DLCQs were evaluated against the existing PLCQ literature
• Study types surveyed: Laboratory analog studies with mock-crime paradigms, as well as field studies with verified ground truth
• Scoring systems considered: Multiple numerical scoring approaches, including the Utah model and computer-based algorithms
• Contextual analysis: Theoretical arguments concerning standardization, ethics, and legal transparency were also weighed alongside empirical outcomes

The authors drew on a body of research that included landmark studies by Raskin, Honts, and their colleagues — researchers who had systematically developed and refined the Utah approach to the CQT over several decades. In 1970, David Raskin began a study of the probable lie comparison question polygraph technique. Raskin and his colleagues systematically refined the elements of polygraphy by determining what aspects of the technique could be scientifically proven to increase validity and reliability — efforts that culminated in what is known today as the Utah approach to the Comparison Question Test.

Results & Key Findings

The headline finding of the review is that directed lie comparison questions produce accuracy and effect sizes comparable to probable lie comparison questions, challenging the long-held assumption that PLCQs are inherently superior. The consensus of studies summarized by Blalock, Nelson, Handler & Shaw (2012) trended towards the conclusion that there is little, if any, real difference in effect size between DLCQs and PLCQs.

Key findings documented across the reviewed studies include:

• Equivalent diagnostic accuracy: Laboratory studies contrasting the two comparison question types failed to reveal statistically significant differences in detection accuracy
• Standardization advantage: DLCQs are more uniform, making the test easier to administer and the results more reliable, and are more straightforward, involving less manipulation of the examinee and reducing the likelihood of testing errors
• Cognitive demand: DLCQs demand more cognitive effort from innocent subjects, enhancing the differences in responses between guilty and innocent parties
• Ethical and legal transparency: The straightforward nature of DLCQs makes them easier to explain to non-specialists, including juries, lawyers, and judges, potentially increasing their courtroom acceptability
• Screening suitability: The review found no empirical basis for restricting DLCQs to diagnostic-only use, supporting their extension into screening contexts

Independent laboratory research cited in the review further corroborated these findings. A large mock-crime experiment contrasting the two question types found substantial main effects of guilt in both computer-scored and human-scored outcomes, F(1, 241) = 143.82, p < .001, ηp² = 0.371 for computer scoring and F(1, 242) = 98.92, p < .001, ηp² = .29 for human scoring, with no meaningful advantage for PLCQs over DLCQs.

Discussion & Significance

The significance of this review extends well beyond a simple comparison of two question types. For decades, the polygraph profession had operated under an implicit hierarchy in which PLCQs were considered the gold standard, with DLCQs occupying a secondary or specialized role. In asserting the superiority of the probable lie comparison question over the directed lie question, critics of DLCQs took a position that is inconsistent with the published scientific evidence. The Blalock et al. review provided the profession with a consolidated, evidence-based counter-argument.

Proponents of PLCQs had argued that the tailored, individualized nature of PLCQs — built around a subject's specific life history and motivated emotional responses — made them more psychophysiologically potent. Although under the controlled conditions of an experiment the probable-lie and the directed-lie variants of the CQT produced equivocal results in terms of detection accuracy, the directed-lie variant has much to recommend it as it is inherently more standardized in its administration and construction.

The review also has meaningful implications for the ongoing theoretical debate about why comparison questions work at all. Many field examiners feel that what makes the question effective and responsive — regardless of whether it is a DLCQ or a PLCQ — is the manner in which the comparison question is introduced to the examinee in the pretest. This perspective suggests that examiner skill in framing and delivering comparison questions may be at least as important as the technical format chosen.

Limitations & Considerations

As a review article rather than a primary study, the paper inherits the limitations of the literature it synthesizes. Key considerations include:

• Laboratory-to-field generalizability: Many studies underpinning the review were conducted in analog (mock-crime) settings where ground truth is known, but stakes are lower than real-world examinations
• Publication bias: Narrative reviews are susceptible to over-representing positive or confirmatory findings if the underlying literature skews toward publication of significant results
• Examiner variability: The standardization advantages of DLCQs assume competent, trained examiners; results may differ with poorly trained practitioners
• Scoring system interactions: The review's conclusions may not apply uniformly across all numerical scoring systems, as different algorithms weight physiological channels differently
• Field data gap: At the time of publication, direct comparisons between DLCQs and PLCQs in verified field (real criminal investigation) contexts remained limited

It is also worth noting that subsequent research on respiration scoring in DLC contexts found nuances not fully anticipated by earlier work. Research has reported that respiration responses to directed lie comparison questions may not result in the expected shorter line excursion with innocent participants compared with responses to target stimuli — yet the implications of those physiological findings for numerical scoring were unexplored at that time.

Practical Applications

For practicing polygraph examiners, the Blalock, Nelson, Handler & Shaw review offers concrete operational guidance: DLCQs are not merely a shortcut or a compromise — they are a scientifically supported alternative to PLCQs with distinct procedural advantages. DLCQs were developed as part of a strategy to improve polygraph testing's effectiveness, particularly in sensitive security settings, with their use notably implemented during the Vietnam Conflict for intelligence screenings. Their contemporary application in both law enforcement and national security screening is therefore grounded in decades of practice and empirical evaluation.

For examiners weighing which comparison question format to deploy, the review supports a pragmatic, evidence-based approach: in contexts where PLCQ development is logistically challenging, where transparency is legally or ethically important, or where standardization across examiners is a priority, DLCQs represent a fully defensible choice. Directed lie comparison questions represent a significant advancement in polygraph technology, offering a more standardized, less intrusive method of detecting deception, and their development and subsequent refinement by researchers have made DLCQs a valuable tool in both security settings and criminal investigations.