Do lie detectors work?

Petition calls for McCanns to take test

www.smithsonianmag.com

Lie Detectors Don't Work as Advertised and They Never Did

"Lie detector." The name has a promising ring, but in reality the polygraph test that we know under that name is anything but.

Leonarde Keeler administered the first lie detector test in a court on this day in 1935. That's 82 years ago. They're still used today in a variety of places, but they've never been proven to work.

In that 1935 case, writes Brandy Zadrozny for The Daily Beast, the machine's readout was considered admissible evidence in court and both prosecutor and defense had agreed to its use.

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How does a lie detector work (if at all)?

The lie detector test is as much as part of the furniture on the Jeremy Kyle show as bad dentistry and low IQ. Lie detectors are not just found in TV studios: they are in police stations, FBI offices and government buildings.

According to Vox, around 70,000 people a year submit to polygraphs while seeking security clearances and jobs with the US government. They are used in police interrogations, to monitor the activities of sex offenders on probation, and even for plea bargains permitted by judges.

When a person takes a polygraph test, they have four to six sensors attached to them. The test starts with the questioner establishing the norms for the person's signals, asking three or four simple questions - for instance, "what is your name?".

When the real questions start, the questioner monitors the moving paper (graph) to detect signals (poly). The signals can be triggered by a faster heart rate, higher blood pressure, or increased perspiration.

Psychology Today argues that the name "lie detector" is as deceptive as the lies it is alleged to detect. The machine - a polygraph machine - actually measures nervous excitement. They consider it "a modern variant of the old technique of trial by ordeal" with not much credibility.

They go even further by comparing it to an ancient Arab test, where a heated knife blade is pressed to the subject's tongue. If he was telling the truth, his tongue would not get burned. The logic was when a person gets nervously excited, their mouth dries because nervousness suppresses salivation. Of course, the subject could be nervous because they have a heated knife in their mouth.

Former police detective Doug Williams calls polygraph machines "insidious Orwellian instrument of torture", capable of sowing fear and mistrust, and ruining careers by tarring truthful people as liars.

In a Supreme Court decision in 1998, ruling against the use of polygraphic evidence in some federal courts, Justice Clarence Thomas said: "There is simply no consensus that polygraph evidence is reliable."

A report from the National Academy of Sciences found that lie detectors work at rates well above chance, though far below perfection. It concluded: "Almost a century of research in scientific psychology and physiology provides little basis for the expectation that a polygraph test could have extremely high accuracy."

Ironically, it is difficult to work out who is telling the truth when it comes to success rates of polygraph machines. The American Polygraph Association argues that they are "highly accurate", with a 90 per cent accuracy rate - whereas some critics say the tests are correct only 70 percent of the time, according to APM Reports.

For a method that makes up a huge part of the Jeremy Kyle show, it is perhaps not surprising that there are conflicting accounts on whether lie detectors works. However, they are not harmless as they are used by authorities to determine guilt and suitability.

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Petition calling for Madeleine McCann's parents to take lie detector test achieves over 25,000 signatures

A petition calling for the parents of Madeleine McCann to take a lie detector test has been signed by over 25,000 people.

The new campaign, which has emerged on website Care2Petitions, calls for Kate and Gerry McCann to take a lie detector test only two months before the 10th anniversary of their daughter's disappearance in Praia da Luz, Portugal.

The petition, which has not been endorsed by the site, claims: 'Whether or not you believe they are part of a cover-up of an accident that took place that fateful night or they are involved in foul play in some way, or indeed they are completely innocent and they have been unfairly targeted, then that is why you MUST sign & share this petition.

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