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Polygraph Tests

December 5, 2006

Lie detector tests are used widely in law enforcement and even in some high-security workplaces. But are they accurate?


Do polygraphs lie? I’m Bob Hirshon and this is Science Update.

Polygraphs supposedly detect lies by measuring changes in sweat, heartrate, breathing and blood pressure. Matthew Loxton of Arvada, Colorado, asked us whether they actually work. We turned to Paul Stern, who directed a study of the polygraph for the National Research Council. Unfortunately, he says the answer’s not clear-cut.

PAUL C. STERN (National Research Council):
It gives some some false positives and false negatives. It has some validity. It clearly does better than chance. It clearly does worse than perfection.

So he says it may be useful in some situations, but only as long as those using the test understand it’s not perfect and make sure to get more evidence for its conclusions.

If you’re looking for the truth behind a science puzzle, call us at 1-800-why-isit. If we use your question on the air, you’ll win a Science Update mug. I’m Bob Hirshon, for AAAS, the science society.