How do lie detector tests work?
The how stuff works links above give a good idea of how they ‘work’. But polygraph tests are an unreliable form of detecting lies. Yes, they do detect lies better than chance. Unfortunately, they also detect a lot of innocent people of lying. In lab experiments, among guilty people, about 75 to 85% of guilty people are shown to be so. Unfortunately, so are 40% of innocent people shown to be guilty. In the real world, what this means is that if there are 100 suspects for a crime, and only one is innocent, about 40 people will be declared guilty based on a polygraph. There is also a high chance that the guilty person will not even be one of the 40 ‘guilty’ people detected by the polygraph. So in essence ‘lie-detectors’ are close to chance alone in their detection of a guilty party. They are highly unreliable.
