Lie detectors are likely lying themselves
It turns out that polygraphy is not only an incredibly inexact science, but that reading the results of a lie detector is almost entirely subjective. In short, lie detectors don't work. But people's lives have been ruined by them.
The problem isn't that the machines don't record something—they do: heart rate, respiration, sweat-gland activity, and so on. But what the changes in those numbers mean is entirely up to interpretation.
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An American Medical Association expert testified before Congress that "the [lie detector] cannot detect lies much better than a coin toss." Further, an article published in the Journal of the American Medical Association by the AMA's Council on Scientific Affairs said in part, "Though the polygraph can recognize guilty suspects with an accuracy that is better than chance, error rates of significant size are possible." Ouch.
A 1997 survey by the American Psychological Association found that psychologists feel that "The use of the polygraph (lie detector test) is not nearly as valid as some say and can easily be beaten and should never be admitted into evidence in courts of law." Eek.
Spot on.
Some people in the far north-east not only watch TV, they believe it.
/johnny