Polygraphs

A polygraph, popularly referred to as a lie detector, measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while a person is asked and answers a series of questions. The belief underpinning the use of the polygraph is that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers. There are, however, no specific physiological reaction associated with lying, making it difficult to identify factors that separate liars from truth tellers. Polygraph examiners also prefer to use their own individual scoring method, as opposed to computerized techniques, as they may more easily defend their own evaluations.

In some countries, polygraphs are used as an interrogation tool with criminal suspects or candidates for sensitive public or private sector employment. US law enforcement and federal government agencies such as the FBI, NSA and the CIA and many police departments such as the LAPD use polygraph examinations to interrogate suspects and screen new employees. Within the US federal government, a polygraph examination is also referred to as a psychophysiological detection of deception (PDD) examination.

The control question test, also known as the probable lie test, was developed to combat the issues with the relevant-irrelevant testing method. Although the relevant questions in the probable lie test are used to obtain a reaction from liars, the physiological reactions that "distinguish" liars may also occur in innocent individuals who fear a false detection or feel passionately that they did not commit the crime. Therefore, although a physiological reaction may be occurring, the reasoning behind the response may be different. Further examination of the probable lie test has indicated that it is biased against innocent subjects. Those who are unable to think of a lie related to the relevant question will automatically fail the test.

Polygraph examiners, or polygraphers, are licensed or regulated in some jurisdictions. The American Polygraph Association sets standards for courses of training of polygraph operators, though it does not certify individual examiners.

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