A polygraph or lie detector examination is a procedure used to determine whether a subject shows the physiological and psychological reactions that are believed to accompany intentional attempts to deceive. Congress has defined both terms in the Employee Polygraph Protection Act of 1988, Pub. L. 100-347, Sec. 1, 29 U.S.C. §§ 2001 et seq. Section 2001(3) defines "lie detector" as including
a polygraph, deceptograph, voice stress analyzer, psychological stress evaluator, or any other similar device (whether mechanical or electrical) that is used, or the results of which are used, for the purpose of rendering a diagnostic opinion regarding the honesty or dishonesty of an individual.
According to Section 2001(4), "the term 'polygraph' means an instrument that--
- records continuously, visually, permanently, and simultaneously changes in cardiovascular, respiratory, and electrodermal patterns as minimum instrumentation standards; and
- is used, or the results of which are used, for the purpose of rendering a diagnostic opinion regarding the honesty or dishonesty of an individual.
Despite the appeal of a mechanical technique to measure a person's veracity, the polygraph has met with limited judicial acceptance and use as a federal investigative tool. In light of present scientific evidence the Department of Justice continues to agree with the conclusion of the Committee on Governmental Operations of the House of Representatives, which held after extensive hearings in 1965:
There is no "lie detector." The polygraph machine is not a "lie detector," nor does the operator who interprets the graphs detect "lies." The machine records physical responses which may or may not be connected with an emotional reaction--and that reaction may or may not be related to guilt or innocence. Many, many physical and psychological factors make it possible for an individual to "beat" the polygraph without detection by the machine or its operator.
H.R.Rep. No. 198, 89th Cong., 1st Sess. 13 (1965). Following further hearings and study, the same conclusions were reached in 1976. The Use of Polygraphs and Similar Devices by Federal Agencies: Hearings on H.R. 795 Before the House Comm. on Government Operations, 94 Cong., 2d Sess. (1976). And in 1988, as a result of continuing doubts about the usefulness and accuracy of polygraphs as a means of detecting deceit, Congress restricted the use of polygraphs in employment decisions. 29 U.S.C. §§ 2001 et seq. Despite Congress's antipathy toward the polygraph, the Department supports the limited use of polygraphs for investigatory purposes.
[cited in JM 9-13.300]