Duration of a polygraph, lie detector test? Why does a polygraph test take so long?
Channel: bearforensics
Date: 26/09/2018

The duration of a polygraph, lie detector test is often misinterpreted. The general public has normally a very simplistic idea of the use of the polygraph. When inquiring about the test people find out that the test has a standard procedure that quite differs from their inital perception. 

This video explains why a polygraph test has a certain duration. The main conceptual error lays in the fact that a polygraph exam does not test questions rather investigate a specific case.

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Why does a test last so long?

The duration of a polygraph test depends on the type of test but on average it usually lasts between 90 and 120 minutes, that is to say between an hour and a half to two hours.

The idea that a polygraph test is just connecting a person to the instrument, ask random questions and the instrument tells where the person is lying, is wrong.

So, why spending so much time if I just want to ask one question, or two? No, it is not a matter of  questions, it is a process that we need to apply to have confidence in the reliability of the test.

The reason why a polygraph test has this duration is due to the preparation for the test. The polygraph examiner needs to understand the case and gather as much information as necessary to be able to elaborate the questions.

Between the explanation of the instrument, test procedure, statement of the examinee and the collection of physiological data, time goes by and an hour and a half to two hours is the normal time of a test.

In summary: “Why does a polygraph test take so long”

1. Follow standard procedure
2. Test an issue/case not questions

Follow predetermined steps to guarantee the reliability of the test
An issue is analyzed and not random questions

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Video produced by Amável Sanches, forensic psychophysiologist, polygraph expert, member of the American Polygraph Association, Primary Polygraph Instructor, major in forensic sciences by the Autonomous University of Barcelona.

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B.E.A.R. FORENSICS