Psychologists debate merits of the polygraph

By Scott Sleek
Monitor staff

Some scientists say the socalled lie-detector test is about as accurate as a palm reading. Others say that even the most pathological of liars haven?t been able to fool it.

Noting this long-standing scientific disagreement about the ability of a machine to tell truth from fabrication, the U.S. Supreme Court has decided, in a case involving a U.S. airman, that polygraph results can be banned from state and federal court proceedings. The 8?1 ruling was handed down in late March.

Now, psychologists on both sides of the polygraph debate are disagreeing about the meaning of the court?s decision. Some say they?re relieved that the court recognized the lack of proof about polygraph reliability.

'The court is saying that a defendant has a Sixth Amendment right to present any ?relevant and reliable? evidence, but that right is not unfettered,' says Brandeis University psychologist Leonard Saxe, PhD, whose research on polygraph fallibility was cited in the court?s opinion. 'If you substituted ?astrological chart? for ?polygraph,? very few people would think it reasonable to present such evidence to a court.'

Psychologists who defend the accuracy of polygraph exams say the decision focused on a narrow constitutional question?a defendant?s right to present a sound defense?and cannot be construed as an outright condemnation of polygraph tests. They note that four justices in the majority said a future case might convince the court to re-examine its position on polygraph evidence.

'All the court did was say that the Constitution doesn?t preclude a jurisdiction from keeping polygraphs out of evidence,' says Charles Honts, PhD, a Boise State University psychology professor and an avid proponent of polygraph testing. 'But that doesn?t mean the evidence has to be precluded.'

The Supreme Court ruling centers on the case of Edward Scheffer, a former U.S. airman who was convicted of illegal drug use after he tested positive for methamphetamines. At his trial, Sheffer tried unsuccessfully to introduce the results of a polygraph test that indicated he did not knowingly ingest illegal drugs. A military appeals court reversed his conviction, saying the military?s automatic ban on polygraphs was unconstitutional.

But the Supreme Court rejected the appeals court ruling, saying the exclusion of the polygraph evidence did not violate Sheffer?s Sixth Amendment right to adequately defend himself. In the majority opinion, Justice Clarence Thomas states that military rules of evidence call for only reliable evidence to be introduced in trial and that scientists and legal experts have never agreed that polygraph results are reliable.

To illustrate the disparity, Thomas cited psychologists W.G. Iacono, PhD, and David Lykken, PhD, who showed the accuracy rate of polygraphs to be barely better than 50 percent. Other researchers, Thomas noted, have pegged the accuracy rate at nearly 90 percent. Thomas and Justices Antonin Scalia, David Souter and William Rehnquist, echoed concerns raised by Saxe and other polygraph critics: Juries could give excessive weight to questionable polygraph results presented as evidence.

But in a concurring opinion, Justice Anthony Kennedy, joined by Justices Sandra Day O?Connor, Ruth Bader Ginsberg and Stephen Breyer, said a future case may show convincing reasons to allow polygraph results in court. Kennedy, as well as Justice John Paul Stevens?the sole dissenter on the ruling?questioned how the federal government can use polygraphs for such tasks as screening personnel in security-sensitive jobs, while prohibiting their use in military trials.

The questions

Debates about the accuracy of the polygraph test have focused not on the technology itself, but on the test questions being given to the people who are hooked up to the device.

Advocates of the tests say that the questions can be designed to provoke revealing psychophysiological reactions, such as perspiration and increased blood pressure, when the person being tested lies. Critics argue that those physical responses have never been proven to be indicators of a person?s dishonesty.

'?Pinocchio? is only a children's story,' argues Saxe, who conducted a study on polygraph reliability for Congress in 1983. 'People do not show a unique and universal bodily reaction when they lie.'

In addition, polygraph examiners?particularly those working in law enforcement settings?often form impressions of a suspect that can bias their interpretation of the test results, notes Israeli psychologist Gershon Ben-Shakhar, a visiting professor at Brandeis University and co-author with Toronto psychologist John Furedy of the book, 'Theories and Applications in the Detection of Deception' (Springer Verlag, 1990). In a study published in 1994 in the Journal of Behavioral Decision Making, Ben-Shakhar and his colleagues found that examiners may indeed be biased when scoring or interpreting polygraph charts, if they have a prior impression of an examinee?s veracity. Police may tell a polygrapher, for example, that they are certain a suspect is guilty, and that may taint the way the polygrapher interprets the suspect?s physiological response to a certain question, he explains.

Among the most commonly used polygraph tests today is the control question test (CQT), used mainly to question criminal suspects. The questions are designed to make innocent subjects doubt their own honesty. Such questions typically focus on common transgressions that people make.

A subject might be asked, 'Did you steal the petty cash from the safe yesterday?' (the relevant question), and then be asked, 'Before you reached age 20, did you ever steal something from your workplace?' (the control question).

The assumption behind the CQT is that truthful suspects will show greater arousal to the control questions than to the relevant questions: The control questions are more difficult to answer with an unqualified 'no.' An honest subject may know for certain that he didn?t steal the petty cash yesterday, but has to stop and think about whether he ever took office equipment home for personal use.

The CQT method, however, is mainly designed to identify non-deceivers rather than liars, psychologists explain. When a subject shows the same reaction to both relevant and control questions, the test is judged inconclusive.

Future outlook

David Raskin, PhD, a retired University of Utah psychologist and one of psychology?s best-known polygraph defenders, says he doesn?t believe the Supreme Court has taken its last look at the polygraph-admissibility issue. He notes that the court doesn?t disparage or reject polygraph testing, but simply points out that scientists disagree on its validity.

'Even Thomas doesn?t come right out and say that polygraphs are inaccurate,' Raskin says. 'He just says that reasonably scientific minds could come to differing conclusions about the test. That?s not an indictment of it.'

Honts, a former student of Raskin?s and editor of The Journal of Credibility Assessment and Witness Psychology, says he believes a compelling case can be made to support the scientific validity of lie-detector results. Studies already show that polygraph results are about as sound as other, admissible forms of forensic evidence, such as ballistics and hair fiber analysis, Honts notes.

Several studies, he adds, have indicated that even the most pathological liars?who may often convince themselves that their lies are true?aren?t likely to pass a polygraph.

'I?ve tested many psychopaths and killers, and when they lie, they all flunk the test,' Honts says.

Critics of polygraph tests agree that the Scheffer opinion centered on a constitutional question. But it nevertheless turned on the fact that polygraphs have no scientific backing, they add.

Recent surveys indicate that most psychologists are skeptical of polygraph exams, Saxe adds. Yet he predicts that polygraph proponents will continue to push for the acceptability of such evidence in the forensic field. And those efforts, he says, reflect people?s constant resistance to ambiguity.

'Polygraph tests keep getting called on because we want to know if ?O.J. did it,? if ?Monica Lewinsky did it,?' he says. 'But the research findings show that, in the real world, you can?t tell who?s lying and who isn?t.'

Further reading
'The validity of the lie detector: two surveys of scientific opinion,' W.G. Iacono and D.T. Lykken, University of Minnesota, Journal of Applied Psychology, 1997, (Vol. 82, No. 3, p. 426?433).
'Psychological Methods in Criminal Investigation and Evidence,' by David Raskin (Springer, 1989).
'Modern Scientific Evidence,' Faigman, et. al. (West, 1997).