A great stressor is being accused of lying when we know we are telling the truth. Whether we are coping with gossip at work, suspicious friends, or dealing with serious issues like criminal accusations, few things get the stress juices flowing more vigorously than someone saying, “I think you’re lying.” In certain serious conditions, we may even be told we should take a polygraph, or “lie detector” test. Media sources say Defense Secretary Pete Hegseth wants Pentagon officials to take a required polygraph test—aka lie detector—to determine if the person leaks information to the press and others. Is this a good strategy? Does the polygraph actually work and detect when someone is lying? The short answer is, “No.” Polygraphs measure physiological changes in such things as respiration, blood pressure, and skin moisture, and it is assumed that these changes in arousal level indicate a person is lying. However, all a polygraph shows are changes in arousal level; whether these changes are indicative of lying is questionable. Studies that investigate the accuracy of the procedure generally show a high error rate (as much as 40%).
The whole concept of the polygraph presents problems. Imagine being hooked up to the machine by an employer and hearing the question, “Have you been stealing from the company?” You may be innocent, but do you think the stressful question might produce a measurable increase in your arousal state when you say, ”No”? If it does, we would have a false positive result—the machine identifies you as a liar. And then, there are your sociopathic types. They can be hooked up to the polygraph and tell you they were born on the planet Neptune and show absolutely no changes in arousal (meaning they must be telling the truth). In this case we have a false negative—the liar is labeled innocent. Either way, we have a problem with the validity of this procedure.
Imagine a company that manufactures nails, and has 500 workers. The owner knows employee theft is occurring, so he hires a polygraph operator to test all 500. The operator tells the owner that his machine is 90% accurate and says, “I won’t get them all, but I’ll identify most of them for you.” Let’s assume that 50 workers are stealing some nails, 450 are not (neither the owner nor operator knows this, of course). When testing the 50 thieves, the 90% machine will correctly identify 45 workers as thieves, and incorrectly label 5 as honest (false negative). When testing the 450 honest employees, 405 will be correctly identified as honest, the other 45 incorrectly identified as thieves (false positive). Note that 90 workers are identified as thieves, and they will be fired. Unfortunately, only 45 of the 90 really are thieves, which means that half the workers who were fired should not have been. The 90% accurate machine gave an accuracy payoff of only 50%!
It’s not a good idea to base important decisions (such as firing an employee) solely on polygraph results. There are too many factors that influence how someone scores, and most of those factors would have nothing to do with the issue at hand. At best, polygraph results should be used in combination with other information gathered about an individual—such as comments to other workers, attendance record, quality of work, lifestyle, and general indicators of company loyalty. Aldrich Ames was a CIA analyst who passed along secret information to the Soviets from 1985 until he was caught in 1993. He passed polygraph testing, with minor inconsistencies being largely ignored. The CIA knew they had a mole, and what led them to Ames was his lifestyle that was inconsistent with his $60K salary: He had his teeth capped; he wore expensive clothes; he paid cash for a $540K home; he bought a $50K Jaguar; the minimum monthly payment on his premium credit cards were more than his monthly salary. It was his financial world that brought him down, not his polygraph results.
Efforts at getting into someone’s private truth-telling will continue, of course, and how successful these efforts will be remains to be seen. A recent development is “brain fingerprinting,” and involves the assumption that only the guilty brain will react to details about the criminal action. As a suspect you might be asked, “Where was the murder weapon found? In a dog house or in a tree house?” Your brain waves might stay stable at the mention of the doghouse, but show irregularities at the mention of the tree house. Uh, oh. The weapon was found in the tree house. You’re screwed even though you’re innocent of the crime. But even here, all is not perfect. How can your interrogators know “tree house” triggered emotion in your brain because it was in a tree house where you first “got lucky” on a romantic night?