Possible Sources of the Difference in the Severity of the Prior Information Effect on Polygraph Scoring Found in Three Published Studies

Abstract

The present article compares three CQT polygraph studies (Elaad et al., 1994; Ginton, 2019; Krapohl & Dutton, 2018), each indicating a different degree of the prior information effect in triggering confirmation bias while scoring polygraph examinations. The comparison led to the conclusion that the sample of the examiners who did the scoring in Krapohl and Dutton’s study (2018) was a better representative of the examiners’ population; however, the robust effect found in it is somewhat questionable since an unspecified part of it could be attributed to uncontrolled contamination of a conformity factor. So, we are left with the findings of the other two studies, which indicate a smaller effect. The comparison between the studies also raised the option that using the conservative inconclusive zone of +/-5 in the numerical scoring might mitigate the prior information impact by reducing the possibility that it may change results from Deception Indicated (DI) to No Deception Indicated (NDI) and vice versa. With such cut scores, at most, the effect would be shown in entering or leaving the Inconclusive zone, which is less problematic in increasing the number of potential errors. The danger of being affected by prior information is still there and should be paid attention to; however, as for now, research evidence indicates that it affects only a small percentage of the total volume of field CQT tests. That is compatible with Ginton’s (2019) findings that the adverse effect in practice may concern less than 5% of the specific event-related CQT examinations.