Polygraphs ('Lie Detectors')

The word polygraph comes from the Greek for "many writings." Polygraph machines, or "lie detector tests," measure physiological information from the body: breathing, blood pressure, and perspiration. The faster the breathing, the higher the blood pressure, and the greater the amount of sweat, the more likely the person being tested is nervous and could be telling a lie.

Below is information on 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 that could measure breathing and blood pressure. He first called his device the "cardio-pneumo psychograph" but began calling it simply "the apparatus" informally.

Larson believed that his invention could help determine whether a suspect was telling the truth. He tested it on 861 subjects in cases over a 3-year period, 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 results of a polygraph test were included as evidence in a criminal case in 1923, they were challenged, and the D.C. District Circuit Court ruled in U.S. v. Frye that polygraph evidence needed to meet certain criteria to be accepted. Known as the "Frye test," it remained the judicial standard in federal courts for 70 years (and remains so in some states).

The court addressed the difficulty of determining just when a scientific discovery (such as the initial invention of the polygraph test) may 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." (Emphasis added in bold.)

In other words, if evidence—such as that obtained from a polygraph machine—it may be admissible.

Inconclusive vs. Incorrect Polygraph Results

Through the years, polygraphs were used by law enforcement agencies but they weren't considered reliable. To begin with, the person who is hooked up to the polygraph would already be quite nervous, and to have tubes placed on the chest, a blood pressure cuff on the arm, and metal plates on the fingers would not relax most people.

There is also a difference of opinion on the accuracy of polygraph tests. The American Polygraph Association has stated that inconclusive polygraph results are not the same as incorrect results. Yet, typically inconclusive readings are figured in with incorrect ones when establishing a percentage of accuracy.

Polygraph experts continued to fine-tune the machines, and also developed a questioning technique that was intended to produce fewer incorrect readings. For example, the subject is asked to respond "yes" or "no" to questions with unrelated questions mixed in with relevant ones. This is meant 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 means 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 on Daubert v. Merrell Dow Pharmaceuticals that replaced the Frye standard. The Court found that judges could admit certain scientific evidence as long as the theory behind it could be tested, had been subject to peer review and publication, the potential error was known, and 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 had 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 it's generally up to the judge.

The polygraph has also been used to pre-screen job applicants or to test employees to measure their truthfulness about such issues as drug use or theft. In 1988, Congress passed the Employee Polygraph Protection Act (EPPA), which prohibits employers from using polygraph evidence to pre-screen employees, test current employees, as the basis for disciplining or firing employees. However, EPPA doesn't apply to government workers.

Learn About Polygraphs and Your Rights From a Local Attorney

Lie detector tests, or polygraphs, seldom find their way into the criminal courtroom. Still, a defendant's having passed a voluntary polygraph test is sometimes a useful tool in a suspect's defense. If you've been charged with a crime where the truthfulness of your testimony will be at issue, your best move is to speak with a local criminal defense attorney as soon as possible.