Supreme Court Weighs Polygraph’s Legal Admissibility

Is the polygraph a reliable “lie detector” that can convict the guilty and free the innocent, or a pseudoscientific fraud that has no place in a court of law?

That is an old question, but it came before the Supreme Court for the first time Monday. The answer has the potential to reshape virtually every trial in the nation.

Polygraph results have been banned from most courts for nearly all of this century. The general rule was set back in 1923 when a federal judge concluded that a rather primitive lie detector, which simply measured changes in a suspect’s blood pressure, was itself suspect and could not be used in court.

But the tide of opinion has shifted recently. Polygraph testing has greatly improved, its advocates say, thanks to computer monitoring of minute changes in a person’s pulse, perspiration and breathing. Some studies have concluded that polygraphs are accurate 90% of the time.

Last year, in a major departure, the U.S. Court of Appeals for the Armed Forces ruled that a defendant has a constitutional right to tell jurors of a polygraph test that indicated he was not lying.

That case is now before the court. If the justices were to affirm the lower-court decision, defendants in every court in the nation--federal and state--would have the right to use favorable polygraph results. Almost surely, prosecutors would seek the same right to use polygraph results showing that a defendant is lying.

The prospects for that happening, however, do not seem good. During oral arguments Monday morning, the justices appeared to agree with a government lawyer who derided polygraphy as pseudoscience based on an unproven theory of deception.

No one questions that a polygraph machine can accurately measure slight changes in a person’s blood pressure or breathing. But no one can prove whether a change means the subject is lying.

“Polygraphy is very different from other scientific evidence,” Deputy Solicitor General Michael R. Dreeben told the court. “It is in essence the opinion of the polygrapher.”

A person who is fearful about being falsely accused could react noticeably to a question involving the accusation, even if he is entirely innocent, the court was told. Similarly, it is impossible to prove that a person who shows no reaction is telling the truth.

With 30 minutes of practice, determined liars can learn such techniques as biting your tongue or pressing your toes against the ground in a way that will register on a polygraph machine, fooling the examiner, Dreeben said.

Still, the government finds itself in an odd position fighting the use of polygraph evidence. Last year, federal agencies administered nearly 35,000 polygraph tests, primarily to people applying for jobs in the FBI, CIA and Defense Department.

The case at hand Monday began in 1992. Airman Edward Scheffer was stationed at the March Air Force Base near Riverside, Calif., when he was accused of writing bad checks and using illegal drugs. A urine test showed that he had methamphetamines in his system.

But when he was given a polygraph test, he denied using drugs and the examiner concluded that there was “no deception” on his part. Scheffer’s lawyers wanted to introduce that evidence during his court-martial, but a 1991 rule promulgated by the Defense Department bars all reference to polygraph results.

On Monday, attorney Kim L. Sheffield, representing Scheffer, noted that the tests “are used in the ordinary course of government business. If this polygraph were so unreliable, why are millions of taxpayers’ dollars being spent for it?”

“That is different,” Dreeben responded. Federal agencies use the polygraph as “an investigative tool” that can signal whether a job applicant is being deceptive. Failing the test will trigger more questioning but will not alone prove that a person is lying, he said.

The justices will issue a ruling in the case (United States vs. Scheffer, 96-1133) in several months.