claimed for polygraph testing can be ascribed to the strength of the expectancy on the part of the examinee that any deception will be revealed by the polygraph. This expectancy can become so strong that it motivates the examinee to admit or confess to crimes or other transgressions. Such admissions are often counted as true positive results of polygraph examinations, even in the complete absence of physiological data or independent confirmation of the admissions. It seems plausible that a belief that is nearly strong enough to lead to a confession may lead to physiological response patterns indicative of deception if the examinee does not confess. If this hypothesis is correct, the polygraph would perform better with examinees who believe it is effective than with those who do not. This hypothesis is, in fact, the rationale for using stimulation tests during the pretest phase of the polygraph examination. Research on the effect of stimulation tests on polygraph accuracy gives mixed results, as is noted in Chapter 5.


Current knowledge about physiological responses to social interaction is consistent with the idea that certain aspects of the interaction in the polygraph testing context may constitute significant sources of systematic error in polygraph interpretation that can affect the specificity as well as the sensitivity of the test, reducing the test’s validity. The usual strategy for addressing systematic error resulting from a testing interaction is to standardize the interaction, perhaps by automating it. However, this strategy might be very difficult to implement effectively, especially with comparison question polygraph testing, because elements of the interaction are integral to creating the expectations and emotional states in the examinee that are said to be necessary for accurate comparison of responses to relevant and comparison questions. Some standardization can be achieved within the comparison question test format—for example, by limiting the examiner’s choice of questions, as is done in the Test of Espionage and Sabotage.

Although much of the knowledge relevant to expectancy effects is decades old, polygraph theory and practice have changed little in terms of their sensitivity to issues of social interaction in the examination setting. Polygraph theory does not give reason to discount the contextual hypotheses concerning possible systematic error.


Psychophysiological detection of deception is one of the oldest branches of applied psychology, with roots going back to the work of

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement