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Do You Swear to Tell the Whole Truth? The Admissibility of Lie Detector Tests

By: LawInfo
One of the greatest challenges for the judge and jury in the courtroom is to determine which witnesses are telling the truth. While witnesses must promise to tell the truth before taking the witness stand, judges and juries often hear conflicting testimony that indicates someone is being untruthful.
 
It might seem like the technology of the polygraph, also known as the lie detector test, could take the guess work out of determining who is lying and who is telling the truth. However, the results of lie detector tests are not always admissible in court.
 
Different Jurisdictions Have Different Rules

The United State Supreme Court has left the question of the admissibility of lie detector evidence up to individual jurisdictions. Different jurisdictions have handled this question differently. Some courts allow lie detector evidence in certain proceedings only or only when both parties agree to its admissibility. Other jurisdictions do not allow lie detector evidence to be entered at all.
 
 
The Argument Against Lie Detector Admissibility

Those who are opposed to allowing the results of lie detector tests to be admitted in court argue that jurors would accept the results of the test without consideration for the test’s accuracy. The accuracy of lie detector test results can vary depending on the person administering the test, the machine used and the person taking the test. They are not always accurate. Jurisdictions which do allow the results of lie detector tests to be considered in court allow each party to present evidence as to why that particular test is or is not reliable.
 
 
The Argument For Lie Detector Admissibility

Those who argue for allowing the results of lie detector tests to be admitted in court argue that the tests are reliable most of the time. Therefore, proponents argue it is useful to prove whether a person is telling the truth or lying. However, many experts disagree with the assumption that lie detector tests are reliable in most situations. Accordingly, when the Supreme Court left the admissibility of lie detector results up to the individual jurisdictions it commented that there is no reliable evidence about the accuracy of lie detector tests.
 
 
How a Lie Detector Works

In order to understand why different courts have different rules about the admissibility of lie detector test results it is important to understand how a lie detector test works. Essentially, the polygraph machine is attached to the person’s body and the examiner asks a series of questions to the person. The test then measures the person’s physiological responses to the questions to determine if he or she is telling the truth.

Although lie detector test results are not always admissible in court, many attorneys and law enforcement officers continue to use the technology when questioning witnesses and suspects. If law enforcement administers a polygraph test to a suspect then they need to issue the Miranda warnings prior to conducting the test.
 
If you have any questions about the use or admissibility of lie detector tests in your jurisdiction then you should contact a local attorney or your local bar association for additional information.
 

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