Exclusive or Nonexclusive Comparison Questions: A Comparative Field Study

Israeli field study comparing exclusive versus non-exclusive comparison question formats in real criminal investigations.

Field study using actual criminal investigations or operational examinations with confirmed outcomes serving as ground truth.

Published in 1999 in Polygraph, 28, 273–283, this study by Amsel and colleagues examined exclusive or nonexclusive comparison questions: a comparative field study. Key findings include: Israeli field study comparing exclusive vs. non-exclusive comparison question formats. Found both formats produced comparable accuracy rates in real criminal investigations. As a field study conducted with real cases, this research provides ecological validity that laboratory studies cannot match.

Format equivalence provides practitioners with flexibility to adapt question construction to specific case circumstances without sacrificing accuracy.

Background & Context

For decades, polygraph examiners have debated a fundamental question about comparison question construction: Should these questions be exclusive (time-barred, as in the Backster technique) or nonexclusive (non-time-barred, as in the Reid technique)? This distinction carries theoretical weight—exclusive comparison questions ask about behavior before a specific age (e.g., "Before age 18, did you ever steal anything?"), while nonexclusive questions span the examinee's entire life (e.g., "Have you ever stolen anything in your life?"). The Backster approach assumed that temporal separation from the relevant issue would enhance the psychological set that makes comparison questions effective.

Amsel's 1999 field study addressed this ongoing controversy using real criminal investigations in Israel rather than laboratory simulations. This ecological validity made the research particularly valuable. The study examined 230 verified Zone Comparison Test field examinations (60% truthful and 40% deceptive), providing one of the first comprehensive field comparisons of these two question formats in actual operational settings.

Research Design & Methodology

The study analyzed 230 verified Zone Comparison Test field examinations from actual criminal investigations, with 87 examinations (37.8%) using exclusive comparison questions and 143 examinations (62.2%) using nonexclusive comparison questions. Ground truth was established through confirmed outcomes—a critical feature that distinguishes field studies from laboratory research where truth status is assigned by experimental design.

Each examination employed two relevant questions, and researchers analyzed field numerical scores to compare physiological responses between the two comparison question formats. The study's distribution—with 60% truthful and 40% deceptive examinees—reflected realistic base rates in criminal investigations rather than the artificial 50/50 splits common in laboratory research. This methodological choice enhanced the study's applicability to real-world polygraph practice.

The study utilized standard numerical scoring procedures to evaluate the strength and direction of physiological responses. By analyzing actual case files with verified outcomes, researchers could assess whether question format influenced the magnitude of differential responses between truthful and deceptive examinees.

Results & Key Findings

Nonexclusive comparison questions produced significantly larger mean numerical scores than exclusive comparison questions. For question one, nonexclusive questions yielded M=2.99 compared to M=2.14 for exclusive questions; for question two, nonexclusive questions produced M=2.87 versus M=2.26 for exclusive questions.

Further analysis of truthful and deceptive subject groups showed that examinations using nonexclusive comparison questions had scores significantly more in the correct direction than those produced by exclusive comparison questions. This finding held across both ground truth categories, suggesting that nonexclusive questions enhanced discriminability between truthful and deceptive examinees rather than simply shifting scores in one direction.

• Sample composition: 230 verified field cases from Israeli criminal investigations
• Exclusive CQ examinations: 87 cases (37.8%) with lower mean scores
• Nonexclusive CQ examinations: 143 cases (62.2%) with higher mean scores
• Ground truth distribution: 60% truthful, 40% deceptive examinees
• Consistent directional accuracy: Nonexclusive questions performed better for both truthful and deceptive subjects

Discussion & Significance

These findings aligned with earlier laboratory studies that examined the same issue, and together presented a strong argument for using nonexclusive comparison questions in conducting specific-issue field examinations. The convergence between laboratory and field results strengthened confidence in the robustness of this effect across different testing environments and populations.

The study challenged long-held assumptions in the Backster tradition that temporal exclusion was necessary for optimal comparison question function. Instead, the data suggested that nonexclusive questions—which encompass the examinee's entire life span and thus overlap temporally with relevant issues—actually produced stronger, more reliable physiological responses. This finding has been subsequently confirmed by multiple researchers, with scientific studies showing no real difference in effect sizes between exclusive and nonexclusive comparison questions (Amsel, 1999; Honts & Reavy, 2009; Horvath & Palmatier, 2008; Horvath, 1988; Palmatier, 1991).

The practical implication is substantial: examiners need not adhere rigidly to time-bar restrictions when constructing comparison questions. This flexibility allows practitioners to adapt question wording to specific case circumstances, cultural contexts, and individual examinee characteristics without sacrificing—and potentially enhancing—diagnostic accuracy.

Limitations & Considerations

While the study's use of actual criminal investigations provided excellent ecological validity, it also introduced methodological constraints inherent to field research. The examiner was not blind to case circumstances, creating potential for expectancy effects. Additionally, the distribution of exclusive versus nonexclusive questions was not randomly assigned but reflected examiner choices, potentially introducing selection bias if certain case types were systematically matched to specific question formats.

The study has attracted criticism from proponents of the Backster technique who argue that test structure deviations may have affected results. Ground truth verification, while superior to laboratory designs, relied on confessions and corroborating evidence that may not be perfectly accurate in all cases. The study was conducted within a specific cultural and legal context (Israeli criminal investigations), and generalizability to other jurisdictions and testing applications requires caution.

Practical Applications

This research liberates examiners from rigid adherence to exclusive comparison question formats when clinical judgment suggests nonexclusive questions would be more appropriate. The finding that the discussion is moot for the exclusive CQ hypothesis as it is not supported by evidence, and field practices have evolved to include both exclusive and nonexclusive CQs as indicated by individual circumstances reflects the study's lasting impact on professional practice.

For consumers of polygraph services, this research provides reassurance that examiner flexibility in question construction does not compromise test validity. Whether an examiner employs time-barred or non-time-barred comparison questions, the fundamental validity of the Zone Comparison Test technique remains intact. Examiners can now prioritize question clarity, cultural appropriateness, and psychological salience over strict adherence to temporal exclusion rules, potentially improving both the testing experience and diagnostic accuracy.