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Good Question: How Effective Are Lie Detector Tests?

MINNEAPOLIS (WCCO) - Ten-year-old Barway Collins has now been missing for a week. On Tuesday, Crystal police called his father a suspect in the boy's disappearance.  They say he failed a lie detector test.

So, how effective are these polygraph tests? Good Question.

"There's no scientific consensus, so they're not effective enough to put into court in most situations," said Mark Osler, a professor of criminal law at the University of St. Thomas. "They don't pass that threshold to be the kind of science we trust enough to put in front of jurors."

The public has debated the effectiveness of polygraphs since they were invented in the early 1920s.  The American Polygraph Association  says scientific research shows they are about 90 percent effective. But, critics, including the American Psychological Association, say it's far less.

"The critics say, at best, they are somewhat better than chance," Osler said.

A polygraph doesn't necessarily detect a lie, but rather detects changes in the body from a person's responses. It measures pulse, heart rate, respiration and skin conductivity, which is a measure of psychological arousal.

"That's part of the uncertainty, because we all respond differently to stress," Osler said. "What we're measuring is the body's reaction and that varies from person to person and that's part of what makes this less than totally reliable."

A review from the National Academy of Sciences found polygraph tests can create a high number of false positive results.

Often, the polygraph test is used as an investigative tool. Many times, the person administering the test is someone trained in interrogation techniques. Osler said the results can vary depending on who is giving the test.

"Part of what interrogators do is exactly that," he said. "They're going to get people to the point where they're going to give answers."

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