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Does the Confession Criterion in Case Selection Inflate Polygraph Accuracy Estimate?

NCJ Number
Polygraph Volume: 32 Issue: 4 Dated: 2003 Pages: 234-244
Donald J. Krapohl; Kendall W. Shull; Andrew H. Ryan
Date Published
11 pages
This article discusses polygraph detectibility of guilty confessing suspects and guilty suspects that did not confess but were caught by other means.
Many polygraph studies have relied on confessions as verification of ground truth. Some critics argue that this creates an overestimation of polygraph accuracy because there is a relationship between polygraph results and the likelihood that a suspect will confess. Among guilty suspects, there could be qualitative group differences between confession and nonconfession cases. In this study, a comprehensive sample of field polygraph cases from a large United States government polygraph program was examined to uncover differences in the polygraph detectibility of guilty confessing suspects, and guilty suspects that did not confess but were caught by other means. The goal was to determine whether there were differences in scores and decisions attributable to the confession criterion. Though none were found, the confession criterion remains a potential source of contamination in undercontrolled studies. The present data demonstrate that it is an overstatement to broadly assert that the confession criterion is a contaminant in a study. The confession criterion is suspected when it leads to samples of cases with nonrepresentative data, such as those with scores more extreme than the population as a whole. It should be relatively straightforward for researchers to collect and report such evidence as others have done so that skewed data can be recognized. 1 footnote, 1 figure, 4 tables, 19 references


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