racy suggested by the lack of false positives would be undercut by the presence of perhaps many false negatives.
All these considerations make it obvious that evaluating the accuracy of the employee screening polygraph is a nontrivial task. It requires more care in defining the criterion than is evident in current practice; it also requires great care in analyzing the evidence.
When the polygraph is used for preemployment screening, defining and measuring accuracy poses additional challenges. In this setting, the polygraph test is being used, in effect, to predict particular aspects of future job performance, such as the likelihood that the examinee, if employed, will commit security violations in the future.3 As is the case for employee screening, defining accuracy requires a clear statement of which specific aspects of future job performance constitute the appropriate criterion. Given such a statement, one way to measure the accuracy of a preemployment polygraph test would be to compare those aspects of job performance among people who are scored as deceptive with the same aspects of performance for people who are scored as nondeceptive. This is impractical if people who score as deceptive are not hired and therefore do not get the chance to demonstrate their job performance. It would be practical, however, to compare the job performance of employees whose scores on the preemployment polygraph varied across the range of scores observed among those hired. In particular, it would be useful to examine the extent to which a person’s score on a preemployment screening polygraph correlated with later instances of target behaviors, such as security violations, that came to the attention of management. We know of no such studies.
Another difficulty in measuring the accuracy of preemployment polygraph tests is that adverse personnel decisions made on the basis of preemployment polygraph examinations are not necessarily due to readings on the polygraph chart.4 For instance, we were told at the FBI that applicants might be rejected for employment for any of the following reasons:
they make admissions during the polygraph examination that specifically exclude them from eligibility for employment (e.g., admitting a felony);
they provide information during the polygraph interview that is not itself a bar to employment but that leads the applicant to be judged deceptive (e.g., admitting past activities that were not disclosed on the job application);
their behavior during the polygraph interview leads to the conclusion that they are trying to evade detection (e.g., the examiner concludes that the applicant is using countermeasures); or