AntiPolygraph.org Message Board

railroaded wrote on Jun 10^th, 2005 at 5:49pm:

In a silent answer test, what is to prevent the examinee from answering a question TRUTHFULLY in his head, even if it would be incriminating if answered verbally? For instance, if I was accused of taking $100 out of a cash register at work and was given a silent answer test, why wouldn't I just think "yes" when asked if I took the money?

Remember that the polygraph does not detect lies or deception. By the rationale of the "silent answer test," it doesn't matter whether or not the subject answers the question truthfully or deceptively in his head, or if he even answers at all. The assumption here is essentially the same as that behind the standard "control question test": that a guilty/deceptive person will feel more threatened by the relevant questions than by the "control" questions and will therefore show a stronger reaction to the former.

Whether or not answering the relevant questions truthfully in one's mind during a "silent answer test" would tend to increase the false negative rate is a question that has not, to my knowledge, been the subject of any competent scientific research.

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Second question: In what situations are GKT's given? Murder, rape, arson? Crimes where there are actual crime scenes?

The Guilty Knowledge Test (also called a Concealed Information Test) may be used in situations where an incident is known to have occurred and investigators have information that would only be known to them and to someone who was involved with the incident. For a good explanation of this technique and how it may be employed, see "The Body on the Stairs: A Pedagogical Detective Story" (chapter 21 of the 1st edition of David T. Lykken's A Tremor in the Blood: Uses and Abuses of the Lie Detector):

http://antipolygraph.org/articles/article-037.pdf

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