Lie detectors generally have a very positive image among people - there's a common perception that they are accurate and reliable. Actually, it would be better to describe it as a misperception because lie detectors are neither accurate nor reliable.

John Ruscio writes in the January/February 2005 issue of Skeptical Inquirer:

An expose on private polygraph firms aired by 60 Minutes in 1986 underscores the subjectivity of the process and its susceptibility to confirmation bias due to the contamination of an examiner's diagnosis with information obtained outside of the formal polygraph test. As summarized by Ben-Shakhar (1991, 236):

Three different polygraph firms were independently called to test an alleged theft of a camera and lens from a photography magazine office employing four employees. In fact, nothing was stolen from the office, but the polygraph examiners were told that it could only have been done by one of the four employees. Each polygraph examiner was told that "it might have been—," with a different employee being fingered in each case (a decidedly weak fingering). In each case, the polygraph examiner identified the "fingered" employee as deceptive, and cleared the other "suspects." Moreover, all polygraph examiners expressed complete confidence in their decisions. This demonstrates not only that polygraph examiners can go wrong, but that their judgment and decision-making processes are infected by a systematic and powerful source of bias, a bias caused by contamination.

Insofar as lie detector tests do reveal information, it seems more likely because either the administrator is an experienced lie detector (there are many people with the training and experience that allows them to reliably sniff out lies) or because the person being tested is made so nervous that they are willing to admit what they have done. Both sorts of cases are certainly an important service, but it's difficult to accept the idea that such a flawed device like a lie detector is necessary to accomplish it.

Lie detectors are made out to sound and appear very scientific, but there is hardly any science whatsoever behind the system. It trades on the popularity of science and technology without having to do any of the hard scientific work itself.

 

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