Barking up the wrong tree

Probably the most comprehensive look at polygraph accuracy is a 2003 report from the National Academy of Sciences. After examining 57 polygraph studies the NAS concluded: "In populations of examinees such as those represented in the polygraph research literature, untrained in countermeasures, specific-incident polygraph tests can discriminate lying from truth telling at rates well above chance, though well below perfection." Their analysis of the 30 most recent polygraph data sets showed an overall accuracy of 85 percent, and an analysis of seven field studies involving specific incidents showed a median accuracy of 89 percent.

For screening purposes, though, the NAS found polygraph tests had too high a margin of error to be genuinely informative. If you made your criteria loose enough to catch most of the bad guys, you were overwhelmed with false positives; if you raised the bar enough to thin out the false positives, you missed too many bad guys.

And what about those countermeasures the NAS mentioned? Yeah, that's a problem too. Because polygraph tests rely on physical reactions, if you can control or mask your reactions at key moments in the questioning, you may be able to throw off the readings enough to produce an inconclusive result. Countermeasure techniques are surprisingly simple: they include discreet physical motions like pressing your toes against the floor or biting your tongue and mental tasks like silently counting backwards from 1,000 by sevens. The goal is to increase your baseline stress level enough to hide any revealing spikes.

If polygraphs are so fallible, why use them at all? In part because testing can intimidate people into confessing, deter bad behavior, and create an impression (however misleading) of vigilance. In other words: security theater.

Source

Given the above, do you think employers should still use them? Still be allowed to use them? Should the government? Should lie-detector results be admissible as evidence?

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