understanding of the physiological measures used in polygraph testing and of the ways they respond to various intentional activities of examinees. Issues of construct validity such as these are likely to arise in courts operating under Daubert and the Federal Rules of Evidence or under analogous state rules, which require that the admissibility of evidence be judged on the basis of the validity of the underlying scientific methods (see Saxe and Ben-Shakhar, 1999).

For polygraph lie detection, scientific validity rests on the strength of evidence supporting all the inferential links between deception and the test results. Inferences from polygraph tests presume that deception on relevant questions uniquely causes certain psychological states different from those caused by comparison questions, that those states are tied to certain physiological concomitants, that those physiological responses are the ones measured by the polygraph instrument, that polygraph scoring systems reflect the deception-relevant aspects of the physiological responses, and that the interpretation of the polygraph scores is appropriate for making the discrimination between deception and truthfulness.1 Inferences also presume that factors unrelated to deception do not interfere with this chain of inference so as to create false test results that misdiagnose the deceptive as truthful or vice versa.

A knowledge base to support the scientific validity of polygraph testing is one that adequately addresses those inferences. It would include evidence that answers such questions as the following:

  • Are the procedures used to measure the physiological changes said to be associated with deception standardized and scientifically valid?2

  • Does the act of deception reliably cause identifiable changes in the physiological processes the polygraph measures (e.g., electrodermal, cardiovascular)?

  • Is deception the only psychological state that would cause these physiological changes in the context of the polygraph test?

  • Does the type of lie (rehearsed, spontaneous) affect the nature of the physiological changes?

  • If the correlation between deception and the physiological response is not perfect, what are the mechanisms by which a truthful response can produce a false positive?

  • Considering such mechanisms, how can the test procedure minimize the chances of false positive results?

  • If the correlation between deception and the physiological response is not perfect, what are the mechanisms by which a deceptive response could produce a false negative result (i.e., mechanisms that would allow for effective countermeasures)?

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