Academic journal article Vanderbilt Law Review

Warping the Rules: How Some Courts Misapply Generic Evidentiary Rules to Exclude Polygraph Evidence

Academic journal article Vanderbilt Law Review

Warping the Rules: How Some Courts Misapply Generic Evidentiary Rules to Exclude Polygraph Evidence

Article excerpt


Polygraph tests rely on the hypothesis that a subject's body yields physiologically different symptoms if he or she is lying.1 When a polygraph test is administered, a mechanical apparatus records the subject's physiological changes, and the polygrapher conducting the examination interprets the data.2 The techniques for measuring physiological changes vary in their foci, which may include respiration, blood pressure, cardiovascular function, and skin resistance.3 The polygraph apparatus4 records changes to one or more of these foci, and a technician, or polygrapher, then analyzes the results to conclude whether the subject has been truthful.

Polygraph results factor into choices ranging from indictment determinations to employment decisions. Between 1981 and 1997, the Pentagon conducted more than 400,000 polygraph examinations.5 Similarly, state law enforcement officers have conducted thousands of polygraph examinations.6 Even in the private sector, where federal law significantly limits private employers from requesting polygraph examinations, employee test results may lead to criminal liability.7

While other segments of society use polygraph results, courts remain reluctant to admit them. Although only two federal circuits employ common law bans against polygraph evidence,8 district courts in every circuit consistently reject polygraph evidence.9 Similarly, many state courts have excluded polygraph evidence for all purposes.10 Unfortunately, many of these courts can only exclude polygraph evidence by warping generic evidentiary rules to act as per se bans.11 This Note focuses on their misapplication of evidentiary rules.

Many criticisms of polygraph evidence have merit, but these concerns should not lead courts to warp evidentiary rules in order to exclude polygraph evidence. For instance, competing studies find various polygraph methods accurate in anywhere from 12.5 to 90 percent of tests,12 but courts should not transpose poor accuracy tests for one testing method to conclude that all other methods are unreliable.13 Similarly, courts may have legitimate public policy concerns that polygraphy could usurp the jury's role as fact-finder,14 but because statutory rules potentially allow polygraph evidence, only legislatively enacted per se bans should properly exclude all polygraph evidence.

Part II of this Note examines how judicial decisions have structured today's case law on the admissibility of polygraph evidence. In Part III, this Note will discuss how courts apply the five prevailing bars to polygraph admissibility: Rules 702, 403, 608, and 704, and per se bans.15 Part IV argues that although each of these bars can properly exclude polygraph evidence in many circumstances, courts should not treat the Federal Rules of Evidence as imposing per se bans on polygraph evidence.


A. Corroborative Scientific Evidence

A polygraph examination forces its subject to recall past events, and the polygrapher then evaluates the subject's physiological responses during this recollection.16 In the adjudicatory setting, nothing prevents the subject from answering the same questions on a witness stand. Polygraph results merely offer those using these tests an evaluation of the subject's veracity in making a particular statement. Although parties in the late 1800s argued that any evidence beyond raw physical evidence and direct testimony was irrelevant,17 such challenges generally fail today. In fact, juries may now hear extrapolations based on data that could not be offered as independent evidence.18 Often, juries may not have the scientific acumen to process such data,19 but they may rely on expert witnesses from each side to parse this information.20 Polygraph results, however, have not received the same deference that courts have given to other types of scientific evidence.

B. …

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