limits of the polygraph, The

Issues in Science and Technology, Fall 2003 by Faigman, David L, Fienberg, Stephen E, Stern, Paul C

The time has come to be truthful about its reliability and usefulness.

Developed almost a century ago, the polygraph is the most famous in a long line of techniques that have been used for detecting deception and determining truth. Indeed, for many in the U.S. law enforcement and intelligence communities, it has become the most valued method for identifying criminals, spies, and saboteurs when direct evidence is lacking. Advocates of its use can plausibly claim that the polygraph has a basis in modern science, because it relies on measures of physiological processes. Yet advocates have repeatedly failed to build any strong scientific justification for its use. Despite this, the polygraph is finding new forensic and quasi-forensic applications in areas where the scientific base is even weaker than it is for the traditional use in criminal trials. This is a very troubling, because these new uses are based on overconfidence in the test's accuracy.

In recent years, and especially since the 2001 terrorist attacks, the U.S. public seems to have become far more willing to believe that modern technology can detect evildoers with precision and before they can do damage. This belief is promulgated in numerous television dramas that portray polygraph tests and other detection technologies as accurately revealing hidden truths about everything from whether a suitor is lying to prospective parents-in-law to which of many possible suspects has committed some hideous crime. Unfortunately, the best available technologies do not perform nearly as well as people would like or as television programs suggest. This situation is unlikely to change any time soon.

Although there is growing pressure from some constituencies to expand the use of polygraph testing in forensic and other public contexts, it would be far wiser for law enforcement and security agencies to minimize use of the tests and to find strategies for reducing threats to public safety and national security that rely as little as possible on the polygraph. Courts that are skeptical about the validity of polygraph evidence are well justified in their attitude.

Legal precedents

An unsuccessful attempt to introduce a polygraph test in a District of Columbia murder case in the 1920s led to a famous court decision. A trial judge's refusal to allow the testimony of William Moulton Marston, who while a graduate student at Harvard had experimented with a method for detecting deception by measuring systolic blood pressure, was appealed. In the 1923 case of Frye v. United States, the circuit court affirmed the trial judge's ruling, stating that, "while courts will go a long way in admitting expert testimony deduced from a well-organized 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. . . We think the systolic blood pressure deception test has not yet gained such standing."

The Frye "general acceptance" test became the dominant rule governing the admissibility of scientific expert testimony for the next 70 years. Most courts refused to admit testimony about polygraph evidence, often with reference to Frye. (Marston, by the way, became prominent not only as a polygraph advocate but as the creator, in 1940, of the first female comic book action hero: Wonder Woman, who was known for the special powers of her equipment, including a magic lasso that "was unbreakable, infinitely stretchable, and could make all who are encircled in it tell the truth.")

In 1993, in the Dauben case, the Supreme Court outlined the current test for the admissibility of scientific evidence in the federal courts. The Daubert test, codified in the Federal Rules of Evidence in 2000, requires trial court judges to act as gatekeepers and evaluate whether the basis for proffered scientific, technical, or other specialized knowledge is reliable and valid. Although Daubert replaced the general acceptance test of Frye, many states, including New York, California, Illinois, and Florida, continue to use Frye. Increasingly, however, courts in Frye jurisdictions are applying a hybrid test that incorporates much of the Daubert thinking. This thinking is consistent with the belief of most scientists that hypotheses gain strength from having survived rigorous testing.

Despite the consistency in basic outlook that evidence such as polygraph tests must be evaluated on the basis of its scientific merit, actual court decisions regarding polygraph use vary widely. In general, courts look at the admissibility of polygraph test resuits in several ways. Many courts, especially state courts, maintain a per se rule excluding polygraph evidence. They do so for reasons ranging from doubt about its scientific merit to concerns that its use would usurp the traditional jury function of assessing credibility. However, a significant number of jurisdictions that otherwise exclude polygraph evidence under a per se rule nonetheless allow the parties to stipulate to the admissibility of the evidence before the test is administered. These courts typically set requirements on matters such as the qualifications of the polygraph examiners and the conditions under which the tests are to be given. It is presumed that the stipulation makes the examinee take the test more seriously and leads to the selection of more impartial polygraph examiners, both factors that produce more accurate results. These assumptions have some commonsense appeal, but they are unsupported by research and don't address whether the accuracy and reliability of neutral polygraph examinations are sufficient to permit them as evidence.