Polygraph Findings

Cesare Lombroso’s (1876/1911) observation of a correlation between deception and changes in pulse and blood pressure laid the basis for the development of the lie detector test. The polygraph is based on the assumption that if a person lies in response to critical questions, an identifiable pattern of changes in respiration, heart rate, blood pressure, and skin resistance can be elicited. Lee (1953) considers the polygraph a useful shortcut that saves time and effort in obtaining a confession from guilty offenders. He cites a number of instances where an offender denied guilt but then confessed after being shown results of a failed polygraph test. According to Lee, “the mere threat of a test accomplished in ten minutes what the sheriff and his deputies were unable to accomplish in 12 days of grilling” (p. 163).

However, Smith (1967) is skeptical of the accuracy of polygraphs, citing many cases of false confessions elicited after positive polygraph findings. He believes that the physiological changes reported are caused by stress rather than deception and that variables such as the examiner’s experience, self-confidence, and attitude play an essential role in the results. Perhaps the most ardent critic of the polygraph is Lykken (1998), who believes that far too many people have been fooled into accepting polygraph findings blindly. Lykken considers the polygraph to be nothing more than pseudoscience, with accuracy no greater than that achieved by the tossing of coins. There is a little dispute that the polygraph measures something; the controversy is whether it detects lying. The consensus in the scientific community is that it is not a reliable and valid measure of lie detection, but it is certainly used frequently to assist in hiring decisions and other types of evaluations where the credibility of a person is in question.

Despite false positive and false negative test results caused by personality and procedural factors, many believe the polygraph can be a useful adjunct in the work of detection when used properly by highly skilled examiners (Yankee, 1995). Infact, Grubin (2010) concludes that “given what we know about the efficacy of polygraph testing with sex offenders, one might argue that it is no longer a question of why we should use it in forensic psychiatry, but why we don’t” (p. 450). The polygraph is not very different from medical instrumentation used in clinical diagnosis; no instrument is perfect, and all laboratory findings must be interpreted and incorporated into the total picture. When medical instrumentation was becoming popular 85 years ago, Cushing (1933) expressed an opinion that is still relevant today and can be applied to the polygraph, namely, that medical findings from instrumentation should be “supplementary [and subordinate] to ... the careful study of the patient by a keen observer” (p. 1571).