Polygraph testing has generated considerable scientific and public controversy. Most psychologists and other scientists agree that there is little basis for the validity of polygraph tests. Courts, including the United States Supreme Court (cf. U.S. v. Scheffer, 1998 in which Dr.'s Saxe's research on polygraph fallibility was cited), have repeatedly rejected the use of polygraph evidence because of its inherent unreliability. Nevertheless, polygraph testing continues to be used in non-judicial settings, often to screen personnel, but sometimes to try to assess the veracity of suspects and witnesses, and to monitor criminal offenderson probation. Polygraph tests are also sometimes used by individuals seeking to convince others of their innocence and, in a narrow range of circumstances, by private agencies and corporations.
The development of currently used "lie detection" technologies has been based on ideas about physiological functioning but has, for the most part, been independent of systematic psychological research. Early theorists believed that deception required effort and, thus, could be assessed by monitoring physiological changes. But such propositions have not been proven and basic research remains limited on the nature of deceptiveness. Efforts to develop actual tests have always outpaced theory-based basic research. Without a better theoretical understanding of the mechanisms by which deception functions, however, development of a lie detection technology seems highly problematic.
For now, although the idea of a lie detector may be comforting, the most practical advice is to remain skeptical about any conclusion wrung from a polygraph.

Cited Research & Additional Sources

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Kozel, F.A., Padgett, T.M. & George, M.S. (2004). A Replication Study of the Neural Correlates of Deception. Behavioral Neuroscience, Vol. 118, No. 4, pp. 852-856.
Lykken, D. (1998). A Tremor in the Blood: Uses and Abuses of the Lie Detector, 2d ed. New York: Perseus.
National Academy of Sciences (2002). The Polygraph and Lie Detection. Washington, DC: National Academy Press.
Saxe, L. (1991). Lying: Thoughts of an applied social psychologist. American Psychologist, Vol. 46, No. 4, pp. 409-415.
Saxe, L. & Ben-Shakhar, G. (1999). Admissibility of polygraph tests: The application of scientific standards post- Daubert.Psychology, Public Policy and the Law, Vol. 5, No. 1 pp. 203-223.

American Psychological Association, August 5, 2004