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The Polygraph and Lie Detection
threshold to use for judging a test result to indicate deception (see Green and Swets, 1966). Such changes do not alter the accuracy of the test. We are referring here to a different phenomenon, in which expectancies alter the social interaction in the test and through this interaction, affect the examinee’s physiological responses in ways unrelated to truth or deception. Such phenomena do alter the accuracy of the test.
This problem may be less serious for concealed knowledge tests than for other test formats because innocent examinees in that format cannot discriminate between relevant and comparison questions. The problem is not completely obviated, however, because extraneous psychological phenomena can differentially affect the responses of examinees who have concealed knowledge and of all examinees in the event that the examiner’s knowledge of the identity of the relevant questions is subtly communicated to them.
In some cases, equipment manufacturers will not reveal exactly what is being measured.
Unpublished letter commenting on the work of Marston, dated December 14, 1917, from John F. Shepard to Major Robert M. Yerkes, attached to minutes of the 6th meeting of Committee on Psychology, National Research Council.