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Polygraph tests are unreliable in detecting lies, as they primarily measure skin conductance which can be easily falsified. Even expert liars can pass the test, while false positives are common. The test can ruin careers and give a false sense of security, leading to laziness in security measures. The assumption that there is a consistent correlation between lying and physiological states is questionable.
There is little or no evidence that polygraph tests can catch liars, and quite a bit of evidence against it. Polygraphs work primarily by measuring the conductance of the skin, which increases when you sweat. But expert liars don’t sweat it. Indeed, numerous double agents and spies in the US government have effortlessly evaded numerous polygraph tests. Other variables measured by the polygraph, including changes in heart rate and blood pressure, can also be easily falsified.
The famous CIA spy for the Soviet Union, Aldrich Ames, passed polygraph tests on numerous occasions. He asked his Soviet manager what to do with these tests, and the operator just laughed: “Don’t worry, they don’t work.” He was right.
Richard Nixon once famously quipped, “I don’t know anything about lie detectors except that they scare the shit out of people.” The law enforcement officers and police officers who use polygraph machines aren’t scientists – they are simply told that the machine can be used to detect lies, given a few weeks of training and merrily on their way, with little reason to wonder what they are saying. Unfortunately, negative results on scientifically invalid lie detector tests can brand someone for life and ruin their career. False positive polygraph tests are common.
In fact, polygraph tests are even more severe for honest people, who aren’t used to having their word questioned. Experienced liars, trained to hide their facial expressions and always appear calm, have the upper hand when it comes to passing the test. Government agencies are given a false sense of security when polygraph tests become mandatory, leading to laziness in other areas of security. This is extremely unhelpful in areas where officers are given and entrusted with sensitive national security information.
The polygraph test is based on a fundamentally questionable scientific assumption: that there is a universally consistent correlation between lying/truth-telling and physiological states. Extensive studies have shown that there is not.
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