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Polygraphs and Lie Detector Tests

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.

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 test and its replacement via the Daubert decision.

Invention of the Lie Detector Test

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."

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 referred to the device as a "lie detector."

During this time, scientists worked at refining Larson's invention. Leonard Keeler, who had worked with Larson as an apprentice, began developing more sensitive polygraph machines in the 1930s, even starting a polygraph school in 1948.

Polygraphs and the Frye Test

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 that polygraph evidence needs to meet specific criteria to be accepted. Known as the Frye test, this remained the judicial standard in federal courts for 70 years and remains so in some jurisdictions as well.

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 as evidence, writing:

"...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."

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.

Inconclusive vs. Incorrect Polygraph Results

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.

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, but inconclusive readings are figured in with incorrect ones when establishing a percentage of accuracy.

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.

The Daubert Standard, Military Trials, and the EPPA

In 1975, federal judges were given more discretion about the admissibility of evidence under the new Federal Rules of Evidence. This meant a judge could allow a jury to consider polygraph results even if they didn't pass the Frye Test.

In 1993, the Supreme Court issued an opinion in Daubert v. Merrell Dow Pharmaceuticals that replaced the Frye standard. The Court ruled that judges could admit certain scientific evidence as long as:

  • The theory behind it could be tested
  • It had been subject to peer review and publication
  • The potential error was known
  • The scientific community in general accepted the theory

In the 1998 case of U.S. v. Scheffer, the U.S. Supreme Court ruled that polygraph tests didn't have to be admitted as evidence in military trials. President George H.W. Bush banned the admission of polygraph evidence from military trials in 1991, citing their unreliability. However, polygraph evidence was not banned outright. Daubert grants judges the right to determine whether polygraph evidence can be used, so in general it's up to the judge.

The polygraph has also been used to pre-screen job applicants or to test employees to measure their truthfulness on issues like drug use or theft. In 1988, Congress passed the Employee Polygraph Protection Act (EPPA). That law prohibits employers from using polygraph evidence to:

  • Pre-screen employees
  • Test current employees as the basis for disciplining or firing them

EPPA doesn't apply to government workers.

Learn About Polygraphs and Your Rights From a Local Criminal Defense Lawyer

Lie detector tests, or polygraphs, seldom find their way into the criminal courtroom. Still, having passed a voluntary polygraph test is sometimes a helpful tool in a suspect's defense. If you've been charged with a crime where the truthfulness of your testimony will be at issue, get legal advice from an experienced criminal defense attorney.

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