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The Polygraph

Most people have heard about polygraph tests, whether it was discussed on their favorite television show or mentioned in a newspaper article they read. However, only a small percentage of people really understand what polygraph tests are.

The word polygraph means “many writings”, which references the way biological responses are recorded during a polygraph test. The subject is usually outfitted with a band over his chest that will monitor his respiratory activity. Sweat gland activity is monitored by two metal plates placed on the subject’s fingers, and cardiovascular activity is monitored by a blood pressure cuff. At no point is a subject’s voice recorded for analysis. Technology that purports to analyze voice stress has not been shown to be reliable. An examiner will use either analog or computerized instruments to record the subject’s physiological data.

After the subject is connected to the machine, the examiner will conduct a pre-test. This involves explaining the testing procedure to the subject, discussing the questions that will be asked, and establishing a baseline. When this has been completed, the examiner will begin the collection phase, during which a series of polygraph charts recording the subject’s responses to the questions will be assembled. The examiner will then study the charts and give an opinion about how truthful the subject has been.

The subject may be given an opportunity by the examiner to explain his or her reaction to certain questions asked during the test, though this is not required.

Who Uses Polygraph Tests?

Polygraph tests are used by:

  • Federal, state, and local law enforcement agencies such as the FBI
  • Agencies in the legal community like the U.S. Attorney offices, District Attorney offices, and defense attorneys
  • Private companies
  • Private citizens

Opponents of polygraph testing often quote low accuracy rates to attack the efficacy of the program. Unfortunately, people who do this typically do not understand how the figures are calculated, particularly when inconclusive tests are involved. When opponents of polygraph tests calculate the accuracy rate, they add in inconclusive tests. For example, an examiner conducts 10 tests. Six are accurate, two are inaccurate, and two are inconclusive. They would calculate the examiner’s accuracy to be 60 percent (6 accurate results out of 10 tests).

The truth is inconclusive test results are exactly how they sound; the examiner was unable to conclude one way or another how honest the subject was being. When this occurs, the subject is usually tested again at a later date and maybe even by another examiner. So the real accuracy score would be 75 percent (6 accurate out of 8 tests).

Inconclusive tests are not held against the examiner, because there are many factors that could have led to that result. Therefore, it is disingenuous to include them in figures highlighting how accurate or inaccurate polygraph tests are.


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