vary substantially across settings in which polygraph tests are used. There is little knowledge about how much these factors influence the outcomes of polygraph tests in field settings. For example, there is evidence suggesting that truthful members of socially stigmatized groups and truthful examinees who are believed to be guilty or believed to have a high likelihood of being guilty may show emotional and physiological responses in polygraph test situations that mimic the responses that are expected of deceptive individuals. The lack of understanding of the processes that underlie polygraph responses makes it very difficult to generalize from the results obtained in specific research settings or with particular subject populations to other settings or populations, or from laboratory research studies to real-world applications.

Evidence on Polygraph Accuracy

Scientific evidence relevant to the accuracy of polygraph tests for employee or preemployment screening is extremely limited. Only one field study, which is flawed, provides evidence directly relevant to accuracy for preemployment screening. A few additional laboratory studies are relevant to preemployment or employee screening, but they are more analogous to specific-incident investigations than to screening because the deceptive examinee is given a precise recent incident about which to lie.

Of the 57 studies the committee used to quantify the accuracy of polygraph testing, all involved specific incidents, typically mock crimes (four studies simulated screening in the sense that the incidents were followed by generic screening-type questions). The quality of the studies varies considerably, but falls far short of what is desirable. Laboratory studies suffer from lack of realism, and in the randomized controlled studies focused on specific incidents using mock crimes, the consequences associated with lying or being judged deceptive almost never mirror the seriousness of these actions in real-world settings in which the polygraph is used. Field studies have major problems with identifying the truth against which test results should be judged. In addition, they suffer from problems associated with heterogeneity and lack of control of extraneous factors and more generally, they have lower quality than could be achieved with careful study design. Moreover, most of the research, in both the laboratory and in the field, does not fully address key potential threats to validity. For these reasons, study results cannot be expected to generalize to practical contexts.

Estimates of accuracy from these 57 studies are almost certainly higher than actual polygraph accuracy of specific-incident testing in the field. Laboratory studies tend to overestimate accuracy because laboratory conditions involve much less variation in test implementation, in the charac-

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