The polygraph test made waves when it first came out, with many people across multiple industries claiming that it was a fool-proof way to detect lies.
However, within weeks of its debut, it already fell under intensive scrutiny. These days, the results of polygraph tests are actually inadmissible in court.
The banning of polygraphs
The National Library of Medicine discusses studies done on the efficacy of lie detector tests. In short, reports found little to no evidence showing that lie detector tests actually performed with any amount of accuracy.
As early as 1998, the U.S. Supreme Court banned the use of polygraph test results in most federal courts because of the findings showing they cannot actually reveal whether someone is lying or not.
The way a polygraph test works is by measuring certain physiological reactions such as breathing, pulse, sweat and blood pressure. Theoretically, a person will exhibit a certain range of activity in each category when lying compared to when telling the truth.
However, in reality, they simply monitor signs of anxiety. No matter whether someone is actually guilty of a crime or not, they will likely feel anxious when under interrogation, nullifying many results with potential false positives.
Why do officers still use them?
Police officers still often use lie detectors in interrogations, though. Why? Not because they believe the results to hold entire accuracy, but because they use it as an intimidation tactic in an effort to gain information from the suspect in more direct ways. Many people will crack under pressure if they believe a lie detector will reveal their lies to law enforcement, giving up that information of their own accord instead.