{"id":352294,"date":"2023-12-11T14:24:23","date_gmt":"2023-12-11T19:24:23","guid":{"rendered":"https:\/\/content.findlaw-admin.com\/ability-law\/criminal\/criminal-procedure\/polygraphs-lie-detectors.html"},"modified":"2023-12-11T14:24:23","modified_gmt":"2023-12-11T19:24:23","slug":"polygraphs-lie-detectors","status":"publish","type":"page","link":"https:\/\/www.findlaw.com\/criminal\/criminal-procedure\/polygraphs-lie-detectors.html","title":{"rendered":"Polygraphs and Lie Detector Tests"},"content":{"rendered":"\n
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Polygraphs and Lie Detector Tests<\/h1>\n
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\n By Lark Lewis, J.D.<\/a> | Legally reviewed by Melissa Bender, Esq.<\/a>\n | Last reviewed\n
\n \n <\/i>\n Legally Reviewed\n <\/summary>\n\n
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This article has been written and reviewed for legal accuracy, clarity, and style by FindLaw\u2019s team of legal writers and attorneys<\/a> and in accordance with our editorial standards<\/a>.<\/em><\/p>\n\n <\/div>\n <\/details>\n\n

\n \n <\/i>\n Fact-Checked\n <\/summary>\n\n
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The last updated date refers to the last time this article was reviewed by FindLaw or one of our contributing authors<\/a>. We make every effort to keep our articles updated. For information regarding a specific legal issue affecting you, please contact an attorney in your area<\/a>.<\/em><\/p>\n\n <\/div>\n <\/details>\n<\/section>\n

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Polygraph machines, or lie detector tests, measure physiological responses from the body, including breathing, blood pressure, and perspiration. The faster you’re breathing, the higher your blood pressure is, and the greater the amount of sweat, the more likely you, as the test subject, are nervous and might be telling a lie.<\/p>\n\n <\/div>\n\n

This article provides information on the invention of the lie detector test. It also discusses the use of polygraphs and lie detector tests in general in the law, including the once-standard Frye<\/i> test<\/a> and its replacement via the Daubert<\/i> decision<\/a>.
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Invention of the Lie Detector Test<\/h2>\r\n

Although it had been suggested for years that physiological changes could help determine whether a person was telling the truth, the first serious effort to apply this information came in 1920. John Larson, a police officer in Berkeley, California, developed a device to measure breathing and blood pressure. Officer Larson called his machine the "cardio-pneumo psychograph" but began informally referring to it as "the apparatus."<\/p>\r\n

Officer Larson believed his invention could help determine whether a suspect was telling the truth. He tested it on 861 subjects in cases over three years, including the key suspect in a highly publicized San Francisco murder investigation. In reporting the story, the San Francisco Call and Post <\/i>referred to the device as a "lie detector."<\/p>\r\n

During this time, scientists worked at refining Larson’s invention. Leonard Keeler<\/a>, who had worked with Larson as an apprentice, began developing more sensitive polygraph machines in the 1930s, even starting a polygraph school in 1948.<\/p>\r\n

Polygraphs and the Frye<\/i> Test<\/h2>\r\n

When the polygraph test results were included as evidence in a criminal case in 1923, they were challenged. The D.C. District Circuit Court ruled in the landmark case of U.S. v. Frye<\/i><\/a> that polygraph evidence needs to meet specific criteria to be accepted. Known as the Frye<\/i> test<\/a>, this remained the judicial standard in federal courts for 70 years and remains so in some jurisdictions as well.<\/p>\r\n

The court addressed the difficulty of determining when a scientific discovery. such as the initial invention of the polygraph test, could be accepted as meeting the standards for admissibility<\/a> as evidence, writing:<\/p>\r\n

"…while the courts will go a long way in admitting experimental testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs."<\/i><\/p>\r\n

In other words, if evidence, such as that obtained from a polygraph machine, is based on science or a theory deemed "generally accepted" by the scientific community, it’s admissible.<\/p>\r\n

Inconclusive vs. Incorrect Polygraph Results<\/h2>\r\n

Through the years, polygraph examinations were used by law enforcement agencies, but they weren’t considered reliable. Just being hooked up to a polygraph machine made most test subjects nervous. Having tubes placed on your chest, along with a blood pressure cuff on your arm and metal plates on your fingers, isn’t relaxing.<\/p>\r\n

There’s also a difference of opinion on the accuracy of polygraph tests. The American Polygraph Association has indicated that inconclusive polygraph results are not the same as incorrect ones<\/a>, but inconclusive readings are figured in with incorrect ones when establishing a percentage of accuracy.<\/p>\r\n

Polygraph experts continued to fine-tune the machines. They also developed a questioning technique intended to produce fewer incorrect readings. For example, the subject is asked to respond "yes" or "no" to questions, with unrelated control questions being mixed in with relevant ones. The intention was to reduce the nervousness effect.<\/p>\r\n

The Daubert<\/i> Standard, Military Trials, and the EPPA<\/h2>\r\n

In 1975, federal judges were given more discretion about the admissibility of evidence under the new Federal Rules of Evidence<\/a>. This meant a judge could allow a jury to consider polygraph results even if they didn’t pass the Frye<\/i> Test.<\/p>\r\n

In 1993, the Supreme Court issued an opinion in Daubert v. Merrell Dow Pharmaceuticals<\/i><\/a> that replaced the Frye<\/i> standard. The Court ruled that judges could admit certain scientific evidence as long as:<\/p>\r\n