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What is a Polygraph Test?

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  • Written By: Diana Bocco
  • Edited By: Bronwyn Harris
  • Last Modified Date: 20 October 2014
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Also known as a "lie detector test," a polygraph test is not something out of the movies. Polygraphs are a common part of criminal investigations and background checks. More and more companies, especially government bodies, now require these tests from potential employees.

A polygraph is a simple machine that consists of six sensors or "wires" that are attached to the person taking the test. The examiner, known as forensic psychophysiologist (FP), observes a sheet of moving paper and the type of lines drawn on it by a special pen. These lines vary according to the emotional reaction of the subject to the questions, and these signals are recorded on paper.

Despite what the name suggests, a polygraph test does not detect lies, but rather evaluates the physical responses of a subject to a series of questions. To do that, it evaluates the subject's heart rate, breathing rate, blood pressure, and the perspiration on his fingertips. Sometimes, a polygraph also evaluates involuntary arm and leg movements and nervous tics, which are often detected during difficult questions. Generally, when a person lies, his or her heart rate increases, he starts sweating, and his whole body reacts. This is what the test measures.

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Before a polygraph test starts, the examiner and the person taking the test will go through a "pretest interview." During this time, the examiner will explain how the test works and review the questions to be asked. In the case of legal issues, a lawyer is usually present during this phase. During the actual test, the examiner asks a mix of irrelevant questions, such as "What is your name?", and questions that are directly related to the issue being tested.

There is a good deal of controversy surrounding lie detector tests, as anybody can learn to cheat them with the proper training and preparation. While the results of a polygraph test can be used in court, many organizations are now fighting to abolish the practice because it cannot be 100% accurate.

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anon281716
Post 3

A polygraph is not acceptable in court, since it does not provide sufficient proof of anything but physical responses.

submariner
Post 2

@ GenevaMech- You brought up an interesting fact about white coat syndrome, and for this very fact, I believe that polygraph lie detector tests should be inadmissible in court. I would assume that being subject to a lie detector test is a nerve wracking experience, and quite a few people show symptoms similar to white coat syndrome when they are nervous. Peoples blood pressure can fluctuate by as much as thirty points from nervousness, so I wouldn't be surprised if these tests have falsely convicted people in the past.

GenevaMech
Post 1

I almost think it would be fun to take a polygraph test just for accuracy's sake. I would probably do horribly, since I get white coat syndrome (blood pressure rises when a doctor walks in the room, but subsides when I calm down), but I would be curious as to how accurate they are. You always see that CIA operatives and other intelligence agents are trained to beat them in movies.

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