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Do lie detector tests really work?

Polygraph probe

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Do lie detector tests really work?

Asked by Lisa Burnham of East London

A lie-detector test or machine is a popular, but inaccurate term for the instrument that records various bodily changes that may provide the basis for a reliable diagnosis of truth or falsehood. The correct term for the instrument is a polygraph.

There is no such thing as a lie-detector, lie-detector test, or lie-detector machine if the terms are taken to mean a mechanical test or device that will produce a clear indication of lying when verbal statements are made.

The polygraph technique, as it is more properly called, measures respiration, blood pressure, and pulse. A supplemental unit that records the galvanic skin response (GSR) is also part of the procedure. The most valuable indicators are respiration and blood pressure and not, as is commonly believed, the sweating palms measured by the GSR.

The polygraph technique is actually more of a diagnostic procedure than a mechanical operation. The competence of the examiner and skillfully controlled questions produce the most meaningful data. Polygraphs do not simply indicate whether a specific statement is true or false. A pattern of response compared to various control questions is evaluated by the examiner to determine the truthfulness of the answers.

Results of the polygraph technique are almost never admissible in court as evidence unless both sides agree in advance to its use. However, it is still used in other places, such as in the workplace, to assess the honesty of employees. Whether the employees can make the boss take one is another matter.

Bootnote

According to Paul Marks writing in the 7 January 2006 New Scientist, the US Department of Defense plans to develop a lie detector that can be used without the subject knowing they are being assessed.

The Remote Personnel Assessment (RPA) device will also be used to pinpoint fighters hiding in a combat zone, or even to spot signs of personal stress that might mark someone out as a terrorist or suicide bomber. The RPA will use microwaves or laser beams reflected off a subject's skin to assess various physiological signs without the need for wires or skin contact. The RPA will focus a beam on a moving or non-moving subject and use the reflected signal to calculate pulse, respiration, or galvanic skin response.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au

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