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Thursday, 1 November, 2001, 11:06 GMT
What gives a liar away?
Do you know when you're being lied to? Probably not, since even experienced police interrogators are no more adept at spotting porkies than the rest of us.

Improve your chances (only moderately, to tell you the truth) with BBC News Online's expert tips.

1) Don't overestimate yourself

"It's extremely hard to spot deception," says Aldert Vrij, author of the research paper Detecting the Liars, just published in The Psychologist.

Mr Vrij points to a study which suggested police officers and lie-detector operators were no better at identifying liars than a control group of students.

It may be that the self-confidence law enforcement professionals had in their abilities to spot a lie actually worked against them - causing them to jump to decisions without properly scrutinising a story or its teller.

2) Don't rely on body language

The so-called "Pinocchio effect" - where liars give themselves away with a "classic" cue such as a hand over the mouth or finger twitching - is mostly the stuff of fairytales.

He will lie even when it is inconvenient: the sign of a true artist

Novelist Gore Vidal
Police forces around the world have long been versed in the art of interpreting twitches, hand movements and changes in voice patterns, "but these cues have never been a good way of detecting deception," says Mr Vrij.

But it is not just in police interview rooms that the Pinocchio myth has its disciples. Poker players devote much energy to noting the "tells" of their competitors.

Famous "tells" include the "shrugging bet" where a player pretends not to care throwing more chips into the pot by giving a nonchalant shrug, when in fact they have a game-winning hand.

Don't bet the farm on hunches like this, is the message from Mr Vrij's more scientific research.

3) Get in quick

Creating a lie on the hoof is actually quite taxing. If you don't give someone sufficient time to concoct an intricate story they are liable to experience increased "cognitive load".

Having to think fast, startled liars actually reduce their hand and other movements as they devote their full attention to seeming "normal". Obviously, this is one exception to the body language rule.

"If people sit very still and rigid and their behaviour appears flat, they may be lying. It's certainly a better indicator than the assertion that a person puts their hand over their mouth when they tell an untruth," says Mr Vrij.

4) Step back from the situation

Formulating and asking questions intended to catch out a liar is also a bit of a mental chore, and one that actually gets in the way of detecting a lie.

I can't tell a lie, Pa; you know I can't tell a lie. I did cut it with my hatchet

George Washington
"Observers" watching the interrogation of a subject are better at spotting lies than the person actually conducting the interview.

Watching a story unfold without having to construct an incisive cross-examination gives you the opportunity to really assess what is being told to you.

Again, pride handicaps the "interviewer", according to Mr Vrij. They tend to over estimate the truthfulness of those they talk to "since they are not very keen to admit they have been fooled by a convincing liar".

5) Raise the stakes

Lucky for the honest souls among us, the more desperately a liar wants to be believed, the worse they are at concealing their deception.

"Oddly, the bigger the stakes and the more motivated the liar the easier it is for observers to find them out."

See also:

16 Mar 01 | UK
MI5 ponders lie-detectors
16 Aug 00 | UK
Guilt written on your face
03 May 00 | Health
How to spot a liar
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