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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I have heard police officers say polygraphs are more accurate than eyewitness accounts. However, I notice they will not accept a polygraph report from a defense attorney showing an accused is innocent unless they are notified in advance that the test is going to be conducted. If a polygraph machine is an accurate “lie detector”, what difference would it make if they know about a test in advance?
If lie dectector tests are so reliable, how come so many criminals can pass them?
Beth,
what makes you believe “so many criminals” are passing polygraph tests?
I heard that some individuals apply clear nail polish on their fingertips, to prevent sweat to be transmitted to the machines, fingers contacts.
Eyewitness accounts are not particularly reliable and they’re easily contaminated. Whether polygraphs are more or less unreliable than an eyewitness is likely moot.
well there not really reliable or unreliable
There’s an urban legend about a study where 1,000 atheists were put on a polygraph, asked if they believed in the existence of God, answered ‘no’ and the polygraph showed they were lying.
Since this would have been a major study with significant implications, no one can say where or when it happened, and it probably would have cost hundreds of thousands of dollars to run, I call shenanigans.