The last-minute accuser of Brett Kavanaugh has splashed all over the Internet and several of my acquaintances have emphatically announced "SHE PASSED A LIE DETECTOR TEST!!!!!" Like that means something significant.
So this article is here to explain the science and procedure behind a polygraph test.
First and foremost, there is no such thing as a "lie detector." A polygraph test is used to try and determine if someone is being deceptive or not. These are two very different things.
Second, the results of a polygraph test are not admissible in a court of law.
A Polygraph machine reads and records your biometric information. Your blood pressure, your heart rate, the electrical conductivity of your skin and your breathing. The readings come out of the machine on a paper strip, much like an electrocardiogram or electroencephalogram.
The procedure starts with the interviewer obtaining a baseline of your data. After you are hooked into the machine they let you sit there quietly for a minute, then ask you test questions where you tell the truth, then you intentionally lie. This gives the interviewer an indication of how your body changes when you are being deceptive. If your heart rate goes up, your breathing changes, your skin conductivity changes (you sweat), or all three or any combination when you tell a lie that you know and the interviewer knows is a lie, during the post-analysis this can mean any question that had a similar result could mean you were being deceptive when you gave that answer.
Any it's not like it's not easy on how to find out how to beat a polygraph test. I am pretty sure I can pass a polygraph test claiming that I killed President Kennedy in Dallas in 1963. According to those who believe lie detectors, the fact that I was two years old and in Cleveland, Ohio at the time would be completely irrelevant and I should be charged with Kennedy's assassination.
Here's the important part. The physiological changes happen when you know you are being deceptive. If you believe you are giving truthful answers, you will not trigger the physiological response that indicates deception. If I were given some incorrect information on a subject I know nothing about (and thus would not doubt the truthfulness of the information) and then asked about that information during a polygraph test, even though my answers would be truthfully wrong, I would not show deception. If you truly believe your answers are truthful, you are not being deceptive. One of my clients in a prior job who was actively schizophrenic totally believed that 1) President Obama's face was on the $1 bill and 2) Obama was his father. You weren't going to get any deceptive indicators from that person on those questions.
I am sure the accuser believes everything she is saying is true and correct. She has convinced herself of those facts in the years since the event. Because of this someone in her position will pass a polygraph test every day of the week and twice on Sunday.