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Mon, July 22

Polygraphs? They're basically useless devices

In May 1978, police arrested four Chicago-area men on charges of murdering a suburban man and raping and murdering his fiancée. All of the suspects said they were innocent, but no real doubt existed about their guilt: Three of them, after all, had failed a polygraph exam.

Eventually, a jury convicted the Ford Heights Four, as the public came to call them, for these brutal slayings, and two of the defendants received death sentences. But in 1996, DNA evidence exonerated all four. They had spent 18 years behind bars, partly because the lie detector lied.

A report issued in October 2002 by the National Academy of Sciences (NAS) recommended that the federal government stop using polygraphs to screen for security risks. Why? Because, in the words of the study, these devices are "intrinsically susceptible to producing erroneous results." That's academese for "I wouldn't trust one as far as I could throw it."

The Energy Department adopted polygraph screening of employees in response to the case of Wen Ho Lee, a scientist who was accused of spying for China but who ended up convicted of only a minor security violation. DOE now tests about 2,000 people a year. But George Mason University systems engineering professor Kathryn Laskey, a member of the NAS committee, noted that "no spy has ever been caught using the polygraph."

Particular dangers lurk in subjecting lots of people to polygraphs in the effort to find a few wrongdoers, because false positives greatly will outnumber "true" positives. Some employees who have done nothing wrong will nonetheless have physiological reactions that look suspicious. Some accomplished liars will be able to fool the machine.

To nab eight out of every 10 real spies, the NAS report found, the device probably would have to erroneously implicate nearly 1,600 people. If its operators set it to minimize false positives, 80 percent of the real spies would slip past. But even then, it would flag 20 innocent people for every guilty one.

The same fallibility that renders these machines unusable for employee monitoring makes them dangerous for criminal investigations as well. Police and prosecutors regard polygraph results as the closest thing to a dead-bang certainty. But that faith lacks any foundation. "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," the panel concluded.

And there is no reason to think that better technology will help. People simply don't respond in a clear and predictable way to questions about what they may have done wrong. The "inherent ambiguity of the physiological measures used in the polygraph suggest that further investments in improving polygraph technique and interpretation will bring only modest improvements in accuracy," said the report. Polygraphs are a crude that's impossible to refine.

The consequences of a misleading polygraph exam are bad enough in the employment arena, where someone can lose a job or not get one. But they're much worse for criminal suspects, who can be locked away or even put to death because their pulse rate rose too much in a stressful situation.

A polygraph result generally can't be used as evidence in court. But some states allow the information if both the prosecution and the defense concur. So prosecutors may offer suspects the opportunity to clear themselves. Innocent suspects sometimes think they have nothing to lose and much to gain from going along – only to fail the test.

In 2002, an Ohio court officially cleared Jimmy Williams after he spent 10 years in prison for the alleged rape of a 12-year-old girl. In fact, the rape never happened, but the Akron man nonetheless managed to fail a polygraph exam. Because his lawyer had agreed in advance to admit the results, the jury heard the lie that the lie detector had implicated him.

Other defendants have been victims not only of the polygraph itself but also its aura of infallibility. Gary Gauger received a death sentence for the murder of his parents on their McHenry County, Ill., farm but was eventually exonerated. He took a polygraph during his interrogation, and the results were inconclusive. But the police told him he had failed it.

Our medieval forebears had their own lie detector test: They dunked suspected witches in water, on the theory that the innocent would sink and the guilty would float. Polygraphs aren't quite as preposterous, but they're bad enough.

E-mail Steve Chapman through the Creators Syndicate Web page at


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