Polygraph Examinations

Are there different types of polygraph examinations?

Several different types of polygraph examinations have been developed; they are the control question test, the relevant-irrelevant test, the directed lie test, and guilty knowledge test.

The control question test (CQT) is the most commonly used test today. With the CQT, control questions are worded to elicit a lie from anyone who takes the test and examiners compare responses to relevant questions with responses from control questions. The CQT rests on the theory that innocent subjects have a stronger response to control questions because they will be nervous and somewhat uncertain about those answers. Liars, it is thought, should have a stronger response to the relevant questions because they must answer these questions dishonestly.

The "Guilty Knowledge Test" (GKT), on the other hand, does not depend upon the subject's emotions. Instead, the GKT depends upon memory and orienting responses. These responses are also referred to as "cognitive processing associated with memory, something that can be determined using psychophysiological procedures." The GKT uses knowledge about a crime only the perpetrator should possess to assess physiological reactions. As in the board game CLUE; only the Butler would know that it was the lead pipe he had in the dining room that fateful night. In this way, a GKT measures involuntary responses associated with memory--generally detecting a response to something unfamiliar. The GKT operator looks to assess the one "correct" or "relevant" answer among irrelevant answers.