evaluate the accuracy of polygraph tests, it is imperative to distinguish several different roles of the polygraph test in polygraph examinations, some of which do not depend on whether the test provides a valid indicator of deception.
One role of the polygraph test is to help elicit admissions from people who believe, or are influenced to believe, that it will accurately detect any deception they may attempt. This role is demonstrated most clearly when a polygraph examination is terminated because of an admission before any charts are done. Such an examination can be thought of as an interrogation interview conducted in the presence of a polygraph. In this case, the polygraph test has a useful role independently of whether it can accurately detect deception: it is effective if the examinee believes it can detect deception. Admissions of this kind provide evidence of the value of the polygraph examination for investigative purposes, but they do not provide evidence that the polygraph test accurately detects deception.
Another role of the polygraph is to test cooperation with an investigative effort. Sometimes a polygraph examination is terminated or leads to an assessment that the examinee is deceptive because of detected or suspected countermeasures during the test.6 If an examinee is judged to be using countermeasures, that is taken as evidence that the examinee is not cooperating with the investigation, particularly if the test protocol asks the examinee not to use countermeasures. Noncooperation is in turn taken as a reason to suspect deception. Holding aside the question of whether such inferences are valid, the use of the polygraph in this way does not depend on the scientific validity of the test.
A third role of the polygraph test is to influence the conduct of a polygraph interview. A polygraph examiner who detects what he or she believes to be deceptive responses during the polygraph test normally conducts the remainder of the interview differently than an examiner who sees no signs of deception. Such an examiner may ask more probing questions, do additional charting, shift to a different type of polygraph test protocol, or take a more confrontational attitude in the interview in an effort to elicit an admission or to “clear” the examinee of suspicion. In this situation, it is impossible without careful experimental analysis to disentangle the effect of polygraph validity from other elements of the interaction in the examination.
Finally, polygraph chart readings may be used directly to make inferences about truthfulness or deceptiveness. Assessments of the scientific validity of the polygraph test as a technique for the psychophysiological detection of deception should properly be made on test outcomes that depend only on chart scoring.7 However, it can be difficult or impossible to consider chart results in isolation because of the likelihood that the examiner’s behavior during the test is affected by prior expectations, the