Scientifically dodgy lie-detector tests may provesurprisingly useful
科學的測謊儀可能驚人的有用
POLYGRAPHS, or “lie detectors”, make frequentappearances on “The Jeremy Kyle Show”, a television programme that resembles nothing somuch as bear-baiting, but with humans. Guests are fond of the tests as a means of provingtheir loved ones' philandering ways, or their own innocence. Now the government seems to begrowing similarly keen.
In May a small number of probation officers began training as polygraph examiners. FromOctober around 1,000 sex offenders released from prison on licence in England and Wales butdeemed to be at high risk of reoffending will be required to undergo polygraph tests. Thechecks 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 toprison but could prompt closer supervision or surveillance.
Polygraphs are used widely in America, including on sex offenders, but in Britain many remainsceptical. Polygraphs do not detect lies. They measure changes in physiology, such asbreathing rate, sweating and blood pressure. Telling lies is often stressful and can promptjumps in the readings. But other things–fear, embarrassment, worries about being wrongfullyaccused–can do the same. Enthusiasts say that polygraphs accurately detect lies 80-90% ofthe time. The British Psychological Society cites studies showing similar figures but cautions thatproblems 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 sexoffenders to reveal more information, before, during and after the test. In a 2010-11 pilotstudy offenders who took polygraph tests made more than twice as many “clinically significantdisclosures”–information that could prompt changes in the way they are managed–as thosethat 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 werebeing honest about their behaviour. Others said that the discussions prompted when they failedthe 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 forensicpsychiatry at Newcastle University who is leading the probation officers' training; they shouldbe 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'sUniversity, Belfast, and give them undue weight. In the government's study, the more testsoffenders took, the fewer lies were flagged. That might indicate that they became moretruthful, 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. Butgetting more information from sex offenders about their behaviour–even on this basis–is still agood thing, suggests Professor Grubin. Instead of Mr Kyle, the government might look to “TheWire”, an American TV drama about murderous gangs, where detectives hooked suspects up tophotocopiers, claiming they were polygraphs.