The Inaccuracy Of Polygraph Tests

Filed under: Criminal Law by Contributor @ October 1, 2013

In television and movies, we have all seen someone’s guilt or innocence definitively proven during the course of a polygraph examination. It seems so believable, with all of the sensors and measurements and lines and graphs. Surely these machines work just as well in real life, right?

In reality, polygraph results are wholly unreliable and should not be used in conjunction with any truth-determining process. Several states (New York, Illinois, D.C., and Pennsylvania) do not allow the results of polygraph tests to be admitted into court whatsoever, and many other states only allow the results if both parties agree to it and if there are disclosures about how fallible the machines are. Opponents of polygraphs say the accuracy of them is about 70 percent, while proponents allege that the accuracy is about 90 percent. Their actual accuracy is likely between these two figures.

Despite their startlingly low accuracy, fifteen federal agencies and many police departments across the country continue to use polygraphs, for multiple reasons. Polygraphs are used to elicit confessions, to make hiring and firing decisions, to test sex offenders who are undergoing psychological treatment or probation, and to rule out suspects during investigation. Even in states which disallow the use of polygraphs in court, e.g. Pennsylvania, detectives and investigators sometimes use polygraph tests to build their case during the investigatory stages. Perhaps more intriguing is the fact that even though the test results will never be admitted in court, the prosecution is often allowed to introduce into evidence things a defendant says during the course of a polygraph examination, be it a confession or other incriminating statement. For this reason no one should ever take a police polygraph examination without first consulting a lawyer.

Polygraph testing may be banned outright one day, but until then it remains a psychological tool that police have at their disposal. Let us know what you think about the use of polygraph testing in the comment section.

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