Should You Take A Lie Detector Test?

Published: 04th April 2006
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Is the standard lie detector test (also known as the polygraph) reliable? Should you be concerned about taking a polygraph test? Let's start with a true story.

The FBI gives agent applicants a lie detector test before hiring them. After 9/11, their polygraph failure rate went to 50%. Did liars suddenly start applying for jobs? No, but the testers were instructed to read the tests differently, even though this meant throwing out some honest people with the few dishonest ones. Imagine what this would do to your future. For all of their lives these mostly innocent people will have a record of a failed FBI polygraph following them.

Most scientists now agree that polygraph "testing" is junk science. In fact, John Larson, one of the pioneers of polygraphic lie detection, says "I'm sorry I ever had any part in it's development." The test is valued by governments and others because it is useful for getting damaging admissions from people, especially those who don't know that the test is a sham.

Unfortunately, the lie detector test is actually biased against the truthful. This is because the more honestly one answers the "control" questions, the more likely one is to fail. Meanwhile, hardened criminals have proven again and again that they can lie throughout the test without detection.

How Lie Detector Tests Work (Or Don't)

The basic idea is this: The polygrapher asks "control" questions in order to get your "baseline responses." These are questions to which the operator knows or assumes the truthful answer. The device measures blood pressure, heart, breathing and perspiration rates. Then, when you are asked other questions (Are you involved in espionage? Did you take Johns watch?) your responses are compared to your baseline responses, to determine if your answer is honest or a lie.

An operator will tell you that you should answer all questions honestly, but they don't actually want this to happen. In fact, they will often ask control questions that they assume you will answer with a lie. This could be something like "Have you ever lied when in trouble?" They may mention that someone who would do such a thing is not a good person, thus encouraging you to lie, so they can see your response.

Operators use this kind of trickery as a standard part of the testing procedure. They also have to use their own judgment. If they think you are dishonest, they may interpret the results differently. Even if they don't do this, they may push harder to find questions that give the result they want. Whether this is conscious or not, it shows how unscientific the whole procedure can be.

Should you take the test? Consider what former CIA Director John M. Deutch had to say about it: "[The CIA's] reliance on the polygraph is truly insane." How about former CIA Director R. James Woolsey: "...the use of this highly flawed instrument should be radically curtailed." You may want to reconsider any plans to take that lie detector test.

Steve Gillman has been hunting down obscure knowledge and useful secrets for years. Learn how to pass a lie detector test and get a free gift at: The Secret Information Site (

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