Nothing like the truth

New Scientist issue 2460, 14 August 2004 (payment required for whole article).

The polygraph is still the most popular tool for ferreting out the guilty. Strange, says David Lykken. Not only is it easy to beat, there is also no evidence that it works

HOW do you tell if someone is lying? Easy, according to many of those who should know the answer, such as US government law enforcement and intelligent agencies: hook them up to a polygraph lie detector. The FBI regularly uses the polygraph in national security investigations, and evidence from it is even admissible in some civilian courts in the US. Now the British government seems to share this optimism about the polygraph’s truth-divining capabilities: last week it revealed it is considering making it mandatory for testing sex offenders.

The trouble is, the polygraph doesn’t work – at least, not in any scientific sense. There is plenty of evidence for its inefficacy. A 2002 report by the US National Academy of Sciences even equated polygraph screening with voodooism. Worse, it can lead to serious miscarriages of justice.