indicators that have no validity. That is, it must add predictive value. It is therefore necessary to define the nonvalid indicators that serve as points of comparison.13

One possible reference point is the level of performance that would be achieved by random guessing about the examinee’s truthfulness or deceptiveness on the relevant questions. In this comparison, the predictive validity of the polygraph test is the difference between its predictive value and that of random guessing. This reference point provides a minimal comparison that we consider too lenient for most practical uses, and particularly for employee screening applications. For the polygraph to have sufficient validity to be of more than academic interest, it must do considerably better than random guessing.

A second possible reference point is the extent to which deception is accurately detected by other techniques normally used in the same investigations as the polygraph (background checks, questionnaires, etc.). Comparisons of the incremental validity (Fiedler, Schmid, and Stahl, in press) of the polygraph consider the improvement provided by the polygraph over other methods of investigation (e.g., background checks). We consider this reference point to be important for making policy decisions about whether to use the polygraph (see Chapter 7), but not for judging validity. The scientific validity of the polygraph is unaffected by whether or not other techniques provide the same information.

A third possible reference point for the validity of polygraph testing is a comparison condition that differs from the polygraph examination only in the absence of the chart data, which is purportedly the source of the valid physiological detection of deception in the polygraph examination. This logic implies a comparison similar to the placebo control condition in medical research. The reference point is an experimental treatment condition that is exactly the same as the one being investigated, except for its active ingredient. For the polygraph, that would mean a test that both the examiner and examinee believed yielded valid detection of deception, but that in fact did not. Polygraph research does not normally use such comparisons, but it could. Doing so would help determine the extent to which the effectiveness of the polygraph is attributable to its validity, as distinct from other features of the polygraph examination, such as beliefs about its validity.

Bogus pipeline research illustrates what might be involved in assessing validity of the polygraph using an experimental condition analogous to a placebo. An actual polygraph test might be compared with a bogus pipeline test in which the examinee is connected to polygraph equipment that, unbeknownst both to examiners and examinees, produced charts that were not the examinee’s (perhaps the chart of a second examinee whose actual polygraph is being read as the comparison to the bogus



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