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The Polygraph and Lie Detection
equate theoretical and scientific base. A solid theoretical and scientific base can give confidence about the robustness of a test across examinees and settings and against the threat of countermeasures and can lead to its improvement over time. The evidence and analysis presented in this chapter lead to several conclusions:
The scientific base for polygraph testing is far from what one would like for a test that carries considerable weight in national security decision making. Basic scientific knowledge of psychophysiology offers support for expecting polygraph testing to have some diagnostic value, at least among naive examinees. However, the science indicates that there is only limited correspondence between the physiological responses measured by the polygraph and the attendant psychological brain states believed to be associated with deception—in particular, that responses typically taken as indicating deception can have other causes.
The accuracy of polygraph tests can be expected to vary across situations because physiological responses vary systematically across examinees and social contexts in ways that are not yet well understood and that can be very difficult to control. Basic research in social psychophysiology suggests, for example, that the accuracy of polygraph tests may be affected when examiners or examinees are members of socially stigmatized groups and may be diminished when an examiner has incorrect expectations about an examinee’s likely innocence or guilt. In addition, accuracy can be expected to differ between event-specific and screening applications of the same test format because the relevant questions must be asked in generic form in the screening applications. Accuracy can also be expected to vary because different examiners have different ways to create the desired emotional climate for a polygraph examination, including using different questions, with the result that examinees’ physiological responses may vary with the way the same test is administered. This variation may be random, or it may be a systematic function of the examiner’s expectancies or aspects of the examiner-examinee interaction. In either case, it places limits on the accuracy that can be consistently expected from polygraph testing.
Basic psychophysiology gives reason for concern that effective countermeasures to the polygraph may be possible. All of the physiological indicators measured by the polygraph can be altered by conscious efforts through cognitive or physical means, and all the physiological responses believed to be associated with deception can also have other causes. As a consequence, it is possible that examinees could take conscious actions that create false polygraph readings.
Available knowledge about the physiological responses measured by the polygraph suggests that there are serious upper limits in principle