Is polygraph testing a futile exercise?

London: Police often resort to lie detector or polygraph test to find out the truth in certain high-profile cases. But is the test really useful? No, says a British psychology researcher.

"Polygraph testing purports to work by detecting anxiety. But are liars more anxious than truth tellers?" said professor Chris Street from University of Huddersfield.

"The reality is no, because often the reason we lie is that telling the truth would be very difficult and more anxiety-provoking than a lie," he explained.

Street added that the British Psychological Society is one body that has dismissed the polygraph as a tool that will never be useful.

"Typical accuracy rates are around 54 percent, reaching up to around 60 percent with training. So there is unlikely to be a one-size-fits-all strategy that gives us accuracy rates anything like what we would want in a legal setting," Street said.

For over 30 years it has been said that we should trust our hunches and unconscious knowledge of body language.

Yet his work shows that we would be better off consciously relying on a single "cue", such as whether or not a person is plainly thinking hard.

"There has been a push in the literature suggesting that indirect lie detection works and the reason is that it is unconscious -- so people should not be making reasoned judgments but relying on their gut feeling," Street said.

"But if our account is correct, that is a very bad way to go," he said.