You Lying Liar: Can You Beat a Polygraph Test?

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A spike in blood pressure, a quickening in breathing, a rise in the electrical conductivity of skin…. These are the signs of a liar, at least, according to a polygraph test. But what if you were telling the truth? 

In television and film, polygraph tests are often depicted as infallible, even if the character themselves do not believe it. In the film Meet the Parents, the main character, Greg, is subjected to a polygraph test (with an antique polygraph device, no less) at the hands of his girlfriend’s father. “These aren’t 100% accurate, right?” he asks. “You’d be surprised how accurate they are. They can tell fairly easily if someone is lying or not,” says the father. Greg’s nervous look says it all, he is going to get caught lying, which is exactly what happens as the needles on the device swing wildly each time he lies. But are polygraphs tests that accurate? Is determining deception as simple as monitoring blood pressure and heart rate? Is there a way to “beat” a polygraph test?

Polygraph Accuracy

Just how accurate polygraph tests are is a hotly debated topic in the scientific community. Polygraph examiners argue the tests are highly accurate and some studies have shown the testing process to be accurate but a 2003 report from the National Academy of Sciences (NAS) casts doubts on polygraph accuracy. The physiological responses the test monitors, for example, are not unique to deception. Blood pressure, heart rate, respiration rate, and skin conductivity are known to change under other emotional states, such as fear or arousal. 

There are also issues with studies of the test’s accuracies. Laboratory studies focused on mock trials, so subjects did not feel the same sense of high stakes as those undergoing polygraph testing for a real trial or as a pre-employment check, and observational field studies were found to be plagued by examiner bias favoring overestimation of polygraph test accuracy. The report also found no evidence of polygraph accuracy across “personality types, sociodemographic groups, psychological and medical conditions, examiner and examinee expectations, or way of administering the test and selecting questions.” An overall recommendation of further scientific study of polygraph testing was the final conclusion of the report.

Faking It

Even if polygraph test accuracy is not currently scientifically backed, it does not mean the tests are inaccurate. Which means subjects undergoing testing are still tempted to cheat the device. Polygraph testing involves the comparison of physiological responses between innocuous questions, such as “Is your name Brad?,” with detailed high-stake questions, such as “Were you involved in the bank robbery occurring on August 12?” If a person can create spikes in physiological responses during truthful answers, it will appear as though they are telling the truth during deceitful answers. 

Countermeasures to beat polygraph tests are seen in several films like Ocean’s 13, where a character hides a tack in his shoes to press down on during truthful answers. This same technique is depicted in the film Harsh Times and the television show Profit, though it is only one of several countermeasures thought to disrupt test results. Subjects might also use drugs, such as Valium, or mental strategies, such as meditation, to counteract rises in physiological responses during dishonest answers. Aldrich Ames, a double-agent for the Soviet Union, passed two polygraph tests by following his handler’s advice to “Get a good night’s sleep, and rest, and go into the test rested and relaxed. Be nice to the polygraph examiner, develop a rapport, and be cooperative and try to maintain your calm.”

Some studies have suggested countermeasures do have an effect on polygraph testing but the NAS report found limitations (most of the studies were conducted by one scientist and his colleagues) and variations (countermeasures increased failed tests in some studies) within the studies. It might also be possible that countermeasures could be detected by the examiners, though there is no direct evidence of this because such information would be kept secret by examiners. Still, the NAS report found subjects trying to beat the test were a concern and warranted more scientific study.

A Complicated Answer

The answers to questions about polygraph testing are complicated. Is it accurate? Maybe, there is a lot to consider about how testing is done, how it is measured, the science behind testing, and so much more. Can you beat a polygraph test? Maybe, more research needs to be done into countermeasures and how they affect physiological responses and test results. Some studies have also shown the test to fail innocent individuals who were honest during the testing process, so the overall answer is polygraph testing is complicated and for a method in use since 1921, the scientific studies are lacking. So, while television and film depict it as accurate, just know the polygraph is still missing some scientific backing – information we bet Greg in Meet the Parents wished he had known.


If you want to learn more about polygraphs and lie detection, grab the free PDF of the NAS report here.

The statements and opinions expressed in this piece are those of the event participants and do not necessarily reflect the views of any organization or agency that provided support for this event or of the National Academies of Sciences, Engineering, and Medicine.