Why Europe Doesn't Use Polygraphs As Lie-Detectors

Polygraphs or "lie detectors", make frequent appearances on "The Jeremy Kyle Show", a television programme that resembles nothing so much as bear-baiting, but with humans.

Guests are fond of the tests as a means of proving their loved ones' philandering ways, or their own innocence. Now the government seems to be growing similarly keen.

In May a small number of probation officers began training as polygraph examiners.

From October around 1,000 sex offenders released from prison on licence in England and Wales but deemed to be at high risk of reoffending will be required to undergo polygraph tests. The checks will help to determine whether offenders have breached the conditions of their licences, such as restrictions on visiting children's playgrounds. Failing a test will not result in a return to prison but could prompt closer supervision or surveillance.

Polygraphs are used widely in America, including on sex offenders, but in Britain many remain sceptical. Polygraphs do not detect lies. They measure changes in physiology, such as breathing rate, sweating and blood pressure. Telling lies is often stressful and can prompt jumps in the readings. But other things-fear, embarrassment, worries about being wrongfully accused-can do the same. Enthusiasts say that polygraphs accurately detect lies 80-90% of the time. The British Psychological Society cites studies showing similar figures but cautions that problems in the research mean that the real rate is probably much lower. And "false positive" rates (dubbing a truthful person a liar) can be as high as 47%.

Boosters of the government's scheme say the point is that using polygraphs encourages sex offenders to reveal more information, before, during and after the test. In a 2010-11 pilot study offenders who took polygraph tests made more than twice as many "clinically significant disclosures"-information that could prompt changes in the way they are managed-as those that did not. Many said they would not have done so without undergoing the test. Jane Wood, a forensic psychologist at the University of Kent who co-authored the report on the pilot, says that some offenders found the tests helpful as way to convince their families they were being honest about their behaviour. Others said that the discussions prompted when they failed the test helped them better to understand the conditions of their licence.

Polygraph tests do not stand on their own, argues Don Grubin, a professor of forensic psychiatry at Newcastle University who is leading the probation officers' training; they should be one of a number of tools used to assess offenders. Nonetheless some remain uneasy. Those using the tests may become complacent, worries Anne-Marie McAlinden of Queen's University, Belfast, and give them undue weight. In the government's study, the more tests offenders took, the fewer lies were flagged. That might indicate that they became more truthful, or it might suggest that they were getting better at gaming the test.

The polygraph's power may rely on offenders' inflated belief in the accuracy of its tests. But getting more information from sex offenders about their behaviour-even on this basis-is still a good thing, suggests Professor Grubin. Instead of Mr Kyle, the government might look to "The Wire", an American TV drama about murderous gangs, where detectives hooked suspects up to photocopiers, claiming they were polygraphs.

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