Validating technique in psychology
One limitation of the GKT is that it can be used only when investigators have information that only a guilty subject would know.The interpretation of "no deception" is also a potential limitation, since it may indicate lack of knowledge rather than innocence.
Some confusion about polygraph test accuracy arises because they are used for different purposes, and for each context somewhat different theory and research is applicable.
This is because control questions are designed to arouse a subject's concern about their past truthfulness, while relevant questions ask about a crime they know they did not commit.
A pattern of greater physiological response to relevant questions than to control questions leads to a diagnosis of "deception." Greater response to control questions leads to a judgment of nondeception.
The most widely used test format for subjects in criminal incident investigations is the Control Question Test (CQT).
The CQT compares responses to "relevant" questions (e.g., "Did you shoot your wife? The control questions are designed to control for the effect of the generally threatening nature of relevant questions.