The truth about polygraph tests: They measure anxiety, not deceit

If you think a polygraph test can reliably tell when someone is lying, think again. While the American Polygraph Association puts the test’s accuracy at 90%, psychologists who have studied the machine in action assert it can only spot a true liar 65%–70% of the time. A polygraph test measures the changes in a person’s heart rate, blood pressure, breathing patterns, and skin conductivity (how much you sweat) in order to detect deception. While these are commonly high during the fight-or-flight response, which is frequently seen when someone tells a lie, they also increase when a person is anxious or afraid. So, even if they are telling the truth, a polygraph could say otherwise simply because of the biological response occurring. Although these tests are still commonly used by law enforcement and other institutions, more and more, scientists are proving they are less than valid and should not be solely relied upon to find the truth.