The reliability of polygraph tests has long vexed judges and scientists alike. California bans the tests in criminal trials; New Mexico doesn't. Some people fool lie detectors. Other studies show a 90 percent rate of accuracy - one reason corporations and government agencies use them often.
The US Supreme Court, however, has never weighed in on the viability of polygraph as a criminal-justice tool.
That changes today when the nine justices hear oral arguments on whether lie-detector evidence can be used by defendants to argue for their innocence. In this case, an airman accused of drug use wants to use an Air Force lie-detector test he took in 1992 to exonerate himself.
Linked to the question of whether he may is another basic issue: Can the government automatically discount an entire range of evidence - polygraphs - from being used in court?
"If the government wins this case, a lot of states will quickly ban polygraph evidence," says Mark Dobson of the Nova Southeastern University Law Center in Fort Lauderdale, Fla.
The issue is not just a matter of legal rules. It has deep constitutional roots. The Sixth Amendment states that "the accused shall enjoy the right ... to have compulsory process for obtaining witnesses in his favor...."
An airman goes AWOL
In 1992, Airman Edward Scheffer began working as an informant for the Air Force Office of Special Investigation (OSI) in a California air base. Mr. Scheffer befriended two civilians who were allegedly dealing drugs. But soon after starting with OSI he wrote $3,300 in bad checks and went AWOL. He was later captured and faced trial on a number of counts, including drug use.
Prior to going AWOL, Scheffer gave a urine sample and took a lie-detector test as part of his OSI work. The urine sample showed traces of methamphetamine. But in a polygraph test he passed, Scheffer said he never used drugs in the Air Force.
In his trial, Scheffer said he had been at the drug dealers' house where large quantities of methamphetamine were present in the kitchen and on the table and that some must have gotten into his food, or was put there.
Under a code of law in military court, polygraph tests cannot be introduced as evidence. Scheffer is challenging that code outright.
In some ways the case, US v. Scheffer, has become a war over studies on the reliability of polygraphs, with both sides marshalling expert views and monographs.
Government briefs point out that factors like sleep, the use of stimulants such as coffee, or stress can alter polygraph outcomes. One study found that physical and mental "countermeasures" that can be taught in 30 minutes - such as biting the tongue, pressing the toes to the floor, or counting backwards - especially when practiced by persons with a strong incentive to cheat, can change test results.
Evidence like DNA, and even handwriting and fingerprints, are better tools, the government argues, partly because they don't involve a subjective interpretation by a test giver.
Scheffer argues that studies cited by the government are outdated and that polygraphy techniques have become sophisticated and refined. A recent Defense Department manual called poly-graphy "clearly one of our most effective investigative tools;" a federal court in 1989 referred to the "tremendous advances" in polygraphy as a reason the FBI, the Secret Service, military intelligence, and law enforcement rely on it. A 1996 survey finds lie detectors detect deception more than 90 percent of the time. That is more accurate, it is noted, than forms of accepted evidence in court such as handwriting analysis, eyewitness accounts, and fingerprints.
Government lawyers will argue that polygraphs could send military tribunals - and even the entire US court system - spiraling into a "battle of polygraph examinations and experts that would impose a burden" on the system, as one brief put it.
US relies heavily on polygraphs
Regardless of the outcome, court watchers are intrigued by one dichotomy in the case: Military and government agencies use the polygraph as a standard practice to make grave decisions about the future of individuals - hiring, firing, discipline, investigation.
Therefore, some critics argue, given the worthiness the government itself places on the polygraph, and its practical everyday use, how could the court deny its use as at least part of a defense in court, especially when the basis for the claim is in the Sixth Amendment itself?