Should polygraph tests be used in court?

Vollmer Institute

Fact Box

  • A polygraph test, or lie detector test, is a machine with four to six sensors that records a person’s breathing rate, pulse, blood pressure, and perspiration to determine if a person is being honest or not during a series of questions. 
  • According to Psychology Today, polygraph tests are 87% accurate. In 2003, the National Academy of Sciences concluded that the efficacy of polygraphs was closer to 75%. 
  • At least 23 states allow polygraph tests to be used in court, but both parties must consent. The tests are more commonly used in civil cases rather than criminal cases. 
  • The ability to detect lies is “no more accurate than chance” with all people: students, psychologists, judges, job interviewers, and law enforcement officers.

Morgan (Yes) 

Polygraph tests—also known as lie detector tests—are examination tools that use a person's bodily reactions to certain questions to determine the truthfulness of their responses. According to BBC News, 'they usually measure things like blood pressure, changes in a person's breathing, and sweating on the palms.' Although decisions in court shouldn't be entirely based on polygraph test results, it's another factor that can support the truth and help a judge or jury come to a conclusion. 

Polygraph tests can be a helpful tool for keeping individuals honest in court. There are additional charges and consequences that come with lying in court, so knowing they are subject to a polygraph test may make someone rethink being dishonest. And while polygraph tests are voluntary, someone who is innocent and telling the truth in court would have no reason to refuse a test because they wouldn't fail. 

In addition, there is a licensed polygraph examiner who administers the test and examines the results carefully to determine the results. They account for variations in each individual's unique response to the questions, which is why polygraph tests are believed to be between 80 and 90% accurate. And while this level of accuracy has been challenged due to the number of factors that can affect polygraph test results, such as general anxiety or medical conditions, polygraph tests are never the sole deciding factor of a person's guilt. Polygraph tests can be used in court as a tool to show honesty—not an absolute indicator of innocence or guilt. 


Noah (No)

For starters, polygraph accuracy has been a question of stark debate for decades. Even though law enforcement uses them, polygraph tests are not reliable. The test results can vary based on the person administering it, the machine used, and the person taking it. Law enforcement agencies use them to gather the information leading to clues and further evidence. Still, prosecutors should not bring the results of the tests themselves to court due to their lack of reliability. For this reason, unless both the plaintiff and defendant agree to it, polygraph results are already outlawed in 32 state courts, and in only 18 states, judges have discretion whether to allow them or not.

Partly due to public perception of polygraph tests, polygraph results have contributed to false confessions. The Innocence Project provided four wrongful convictions when officials convinced them the individual, they had failed their polygraph, leading to a coerced confession and subsequent wrongful conviction. Further still, The Innocence Project tells us that some polygraph examiners do not even have their work reviewed by others and do not follow national protocols for administering the tests.

Ultimately this is an issue about what justice means to us as citizens. Justice is not properly served if an arbitrary test with unreliable results is presented as hard and factual evidence in the court because it simply is not. If the prosecutor or the defense's case hinges on the results of a polygraph, it is as reliable as the test itself—that is to say, not at all.

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