world settings in which the polygraph is used. Polygraph practitioners claim that such studies underestimate the accuracy of the polygraph for motivated examinees, but we have found neither a compelling theoretical rationale nor a clear base of empirical evidence to support this claim; in our judgment, these studies overestimate accuracy. Virtually all the observational field studies of the polygraph have been focused on specific incidents and have been plagued by measurement biases that favor over-estimation of accuracy, such as examiner contamination, as well as biases created by the lack of a clear and independent measure of truth.

Overestimation For the reasons cited, we believe that estimates of polygraph accuracy from existing research overestimate accuracy in actual practice, even for specific-incident investigations. The evidence is insufficient to allow a quantitative estimate of the size of the overestimate.

Estimate of Accuracy Notwithstanding the limitations of the quality of the empirical research and the limited ability to generalize to real-world settings, we conclude that in populations of examinees such as those represented in the polygraph research literature, untrained in countermeasures, specific-incident polygraph tests for event-specific investigations can discriminate lying from truth telling at rates well above chance, though well below perfection.

Accuracy may be highly variable across situations. The evidence does not allow any precise quantitative estimate of polygraph accuracy or provide confidence that accuracy is stable across personality types, sociodemographic groups, psychological and medical conditions, examiner and examinee expectancies, or ways of administering the test and selecting questions. In particular, the evidence does not provide confidence that polygraph accuracy is robust against potential countermeasures. There is essentially no evidence on the incremental validity of polygraph testing, that is, its ability to add predictive value to that which can be achieved by other methods.

Utility Polygraph examinations may have utility to the extent that they can elicit admissions and confessions, deter undesired activity, and instill public confidence. However, such utility is separate from polygraph validity. There is substantial anecdotal evidence that admissions and confessions occur in polygraph examinations, but no direct scientific evidence assessing the utility of the polygraph. Indirect evidence supports the idea that a technique will exhibit utility effects if examinees and the public believe that there is a high likelihood of a deceptive person being detected and that the costs of being judged deceptive are substantial. Any technique about which people hold such beliefs is likely to exhibit utility, whether or not it is valid. For example, there is no evidence to suggest that admissions and



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