Everyone has experienced a moment when they wondered if someone is lying. From personal problems to big national news stories, it’s impossible to tell if someone is being honest or not. That’s why the lie detector test has always captured people’s imaginations as a device that could send criminals to jail, expose cheaters, and help the truth always win out.

In movies and TV lie detector tests always seem to help the good guys win out, but these machines actually exist. The real question is, how accurate are lie detectors?


An Important Distinction

ABC news has made it clear that lie detector might not be the right word. Frank Horvath of the American Polygraph Association is quick to point out that, “There is no test that can detect lies.” The technical name for lie detector tests is a polygraph test. Polygraph machines record several different aspects of a person while they are asked different questions, such as respiratory rate, sweat gland activity, and cardiovascular activity. Then, examiners monitor this data to try and determine if a person is lying.  So, if you’ve been wondering how reliable are lie detectors? The answer is a lot more complicated than you might expect.


The Numbers

Most experts agree that the accuracy of a polygraph will change depending on whom you are talking to. Proponents for the machine will say that it is 90 percent accurate and critics will say it is only about 708 percent accurate. The reason for this disparity is that the test itself is highly subjective and dependent on the person being examined, the examiner, and the machine itself.

But, even with all of this potential for problems, NPR recently reported on Doug Williams, who claimed to be able to train people to fool the polygraph test. Williams does this because he is a strong proponent against the use of the polygraph because of its inaccuracy. However, a National Academy of Sciences review was conducted in 2002 to determine the accuracy of lie detector tests, and their official conclusion was that the test is far better than chance in detecting lies.

With some saying that the accuracy of lie detectors ranges above 80 percent and others saying that it is significantly lower than that, it’s difficult to determine an exact success rate. But, most experts would agree that it’s a useful tool to help people where otherwise there is almost nothing else but pure guesswork.