To measure criterion validity, it is necessary to have a clearly defined criterion. The appropriate criterion depends on whether the polygraph is being used for event-specific investigation, employee screening, or preemployment screening. For event-specific investigation, the polygraph is intended to measure the examinee’s truthfulness about a specific incident. The accuracy of the polygraph test is the correspondence of the test outcome with actual truthfulness, which in this context is easy to define (although not necessarily to ascertain). Thus, measurement of accuracy in the specific-event case is straightforward in principle. It can be difficult in practice, however, if there is no way of independently determining what actually occurred.

Measuring accuracy in the employee screening polygraph setting raises more difficult issues. The Test of Espionage and Sabotage (TES) polygraph examination commonly used for screening at the U.S. Department of Energy weapons laboratories is intended to test whether an individual has committed espionage, engaged in sabotage, provided classified information to an unauthorized person, or had unauthorized contact with a foreign national. The examination asks whether the examinee intends to answer the security questions truthfully and whether he or she has engaged in any of the target behaviors. Accuracy of this screening polygraph might be defined as the extent to which the polygraph scoring corresponds to actual truthfulness of responses to these target questions. It might also be defined for a multi-issue polygraph screening test as the extent to which the test results correctly identify which of the target behaviors an examinee may have engaged in.

These seem straightforward criteria at first glance. However, there often is a large class of events that may be relevant to the examination, and it may not be clear to the examinee which of these is intended to be covered. For example, if asked whether one has ever provided classified information to an unauthorized person, one employee might have an emotional reaction brought on by remembering an incident in which he or she failed to properly wrap a classified report for a one-minute trip outside a secured area. Another employee might not have such a reaction. Such an event is a security violation, but individuals may differ about how serious it is and how relevant it is to the test question.

The U.S. Department of Energy (DOE) has developed guidelines regarding the behaviors that are and are not covered by TES questions, which probably resolve many ambiguities for examinees (a detailed description of how the terms espionage and sabotage are explained to examinees in research uses of the TES appears in Dollins [1997]). However, there appear to be ambiguous, even inconsistent definitions for the target of the TES for examiners. Agency officials repeatedly told the committee that the counterintelligence program at DOE is intended to identify serious

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