1. the scoring of the polygraph chart supports an assessment that the applicant is deceptive.

Only the last of these reasons is unambiguously a function of the physiological responses measured by the polygraph.5 For the other reasons, the chart itself is only one input to the decision-making process. The relative importance of physiological responses, interrogation technique, and astute observation by an examiner is difficult to determine and is rarely explored in research. These distinctions may not be considered important for judging the usefulness or utility of polygraph examinations as screening tools, but they are critical if the personnel decisions made on the basis of the polygraph examination are to be used for measuring accuracy.

There are difficulties with using polygraphs (or other tests) for preemployment screening that go beyond accuracy. Perhaps most critical, it is necessary to make inferences about future behavior on the basis of polygraph evidence about past behaviors that may be quite different in kind. The construct validity of such inferences depends on specifying and testing a plausible theory that links evidence of past behavior, such as illegal drug use, to future behavior of a different kind, such as revealing classified information. We have not found either any explicit statement of a plausible theory of this sort in the polygraph literature or any appropriate evidence of construct validity.

A CONSISTENT APPROACH TO MEASURING ACCURACY

For choosing appropriate measures of accuracy it is helpful to consider the polygraph as a diagnostic test of truthfulness or deception and the criterion as consisting of independent indicators of what actually occurred. In this respect, the polygraph is similar to other diagnostic tests; the scientific work that has gone into measuring the accuracy of such tests can be applied to measuring the accuracy of the polygraph. This section draws on this scientific work and explains the measure of accuracy we have chosen for this study. It introduces a number of technical terms that are needed for understanding our measure of accuracy.

Diagnostic tests generally result in a binary judgment—yes or no— concerning whether or not some condition is present. The tests themselves, however, usually give more than two values. For example, cholesterol tests give a range of values that are typically collapsed into two or three categories for purposes of medical decision: high risk, justifying medical intervention; low risk, leading to no intervention; and an intermediate category, justifying watchful waiting or low-risk changes in diet and life-style, but not medical intervention. Polygraph tests similarly



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