tests might elicit admissions to acts not central to the intent of the question and these answers might be judged either as successes or failures of the test. In this regard, we have seen no indication of a clear and stable agreement on criteria for judging answers to security screening polygraph questions in any agency using them.

The use of polygraph testing for preemployment screening is even more complicated because it involves inferences about future behavior on the basis of information about past behaviors that may be quite different (e.g., does past use of illegal drugs, or lying about such use on a polygraph test, predict future spying?).

The committee’s charge was specifically “to conduct a scientific review of the research on polygraph examinations that pertains to their validity and reliability, in particular for personnel security screening,” that is, for the second and third purposes. We have focused mainly on validity because a test that is reliable (i.e., produces consistent outcomes) has little use unless it is also valid (i.e., measures what it is supposed to measure). Virtually all the available scientific evidence on polygraph test validity comes from studies of specific-event investigations, so the committee had to rely heavily on that evidence, in addition to the few available studies that are relevant for screening. The general quality of the evidence for judging polygraph validity is relatively low: the substantial majority of the studies most relevant for this purpose were below the quality level typically needed for funding by the National Science Foundation or the National Institutes of Health.

SCIENTIFIC EVIDENCE

Basic Science

Almost a century of research in scientific psychology and physiology provides little basis for the expectation that a polygraph test could have extremely high accuracy. Although psychological states often associated with deception (e.g., fear of being judged deceptive) do tend to affect the physiological responses that the polygraph measures, these same states can arise in the absence of deception. Moreover, many other psychological and physiological factors (e.g., anxiety about being tested) also affect those responses. Such phenomena make polygraph testing intrinsically susceptible to producing erroneous results. This inherent ambiguity of the physiological measures used in the polygraph suggests that further investments in improving polygraph technique and interpretation will bring only modest improvements in accuracy.

Polygraph research has not developed and tested theories of the underlying factors that produce the observed responses. Factors other than truthfulness that affect the physiological responses being measured can