Polygraph examinations are not the only source of information used to determine an examinee’s truthfulness or deceptiveness. In event-specific investigations, a variety of techniques of criminal or security investigation are used, and it is often these that lead to the selection of the individuals (suspects) for polygraph testing. In pre-employment screening, employment questionnaires and interviews, as well as background checks, may supplement information from polygraph tests. In employee screening, periodic or occasional polygraph examinations may be supplemented by interviews and investigations, especially if the polygraph test result is inconclusive or shows a significant response that remains unexplained. In short, information from polygraph examinations may be combined in many ways with information from other sources in judging truthfulness or deception. Policy decisions on the use of the polygraph must therefore consider not only the information that can be gained from the polygraph alone, but also the value it may add to what can be learned from other available investigative techniques. Furthermore, besides the additive value of polygraph information, the polygraph test may influence or be affected by other forms of investigation in known and unknown ways. For example, evidence about a crime may identify certain suspects who are then given a polygraph test, or a polygraph test result may lead an ongoing investigation to focus on one person and turn away from others. Such interactions can make it difficult to separate the effects of the polygraph test from those of concurrent investigative methods.
The value, or utility, of polygraph testing does not lie only in its validity for detecting deception. It may have deterrent value, for instance, if people do not take certain actions because they fear that a polygraph examination will uncover them. It may help focus an investigation on particular aspects of a case highlighted by an examinee’s physiological responses. And, as noted above, polygraph testing may elicit admissions or confessions of undesired activity from people who believe they are better off to admit certain activities voluntarily than to submit to a polygraph test and risk being accused of these or more serious activities, as well as being accused of deception. These admissions or confessions may occur during the polygraph examination, either before charts are collected or in response to an examiner’s questions about the charts. These kinds of utility do not depend on validity in the sense that polygraph policies may yield deterrence, admissions, and confessions when a potential examinee believes that the polygraph will detect or has detected deception, even if scientific evidence does not support such a belief.9 We discuss utility in more detail in Chapter 2, along with its relationship to the investigation of validity.