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2 Overview of Key Supreme Court Decisions The Daubert case was by no means the first proceeding in which the courts had to struggle with the challenge of deciding when and which scientific expertise is needed to decide a case. In the past 30 years there has been an increase in toxic tort litigation, that is, cases in which the plaintiffs bringing the action allege that their injuries or diseases have been caused by exposure to the defendant's product or discharge. These cases have received a great deal of attention, in part because they often involve claims of significant injury, demands for large amounts of money, and allegations that some of the expert testimony did not meet appropriate scientific standards. Daubert was the first of three Supreme Court cases that significantly shaped the way in which federal courts would evaluate scientific testimony. All three cases centered on the admissibility of expert testimony concerning the data required to establish causa- tion, an exercise that involves synthesis of available evidence, and all three cases recognized that expert testimony must be subject to a strong and careful judicial gatekeeper function. The most recent of the three, Kumho Tire Co. v. Carmichael, while involving causation, was not a toxic tort case. For 70 years, many federal courts relied on the general acceptance standard laid out in Frye v. the United States (1923) to determine the admissibility of expert testimony. Under the Frye standard expert testimony is admissible only if its methodology is "generally accepted" (i.e., a consensus has been reached) in the relevant scientific community. The Daubert decision essentially 3

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DISCUSSIONS OF THE COMMITTEE ON DAUBERT STANDARDS held that Frye did not survive the enactment of the Federal Rules of Evidence, and interpreted Rule 702 of the Federal Rules of Evidence as requiring that scientific expert testimony be grounded in the methodology and reasoning of science (i.e., the expert must show the underlying validity of his opinion). In finding that the epidemiological and toxicological evidence offered by the plaintiff experts was inadmissible, the lower court in Daubert had applied the Frye general acceptance test. However, the Supreme Court spelled out a new test for the admissibility of scientific evidence, aimed to ensure that it "is not only relevant, but reliable." The Daubert case was one of many in which plaintiffs claimed that birth defects exhibited by their children were caused by Bendectin, an anti-morning sickness pill that had been taken by their mothers (and approximately 20 million other pregnant women). In response to these suits, the defendant manufacturers took the drug off the market even though it never lost its Food and Drug Administration approval. A central message of the Daubert decision was the Court's designation of the trial judge as the gatekeeper, responsible for screening expert testimony to determine whether the relevancy and reliability requirements are met. In the second part of his majority opinion, over the dissent of Chief Justice Rehnquist and Justice Stevens, Justice Blackmun wrote that federal judges have a duty to ensure that "an expert's testimony rests on a reliable foundation and is relevant to the task at hand." He suggested that the reliabil- ity of scientific testimony be judged using the following criteria: 1) whether or not it could be tested and falsified; 2) whether it had been subject to peer review and publication; 3) whehter there existed known or potential rate of error and standards controlling the technique's operation; and 4) whether or not it was generally accepted within the scientific community. However, Blackmun emphasized the flexible nature of this reliability requirement, a point that would be reiterated in a later decision (Kumho). To satisfy the reliability standard, the experts' opinion must be the product of 4

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Overview scientific reasoning and methodology. This requirement reinforces the concept of science as an empirical endeavor. The Court also stated that the testimony must be relevant, that is, it must fit the facts of the case. The expert may not testify about a hypothesis that cannot be applied to the facts under consideration. A second case provided courts with additional guidance. In General Electric v. Joiner (1997) a plaintiff who was a longtime smoker with a family history of lung cancer claimed the exposure to polychlorinated biphenyls (PCBs) had promoted the development of his small-cell lung cancer. Relying on the Daubert criteria (de- scribed previously), the trial court excluded the plaintiff's expert testimony and granted summary judgment. The intermediate appellate court reversed the lower court decision. The Supreme Court then held that in reviewing a trial judge's evidentiary ruling an appellate court must use an abuse of discretion standard, which requires the reviewing court to defer to the rulings of the trial court unless they are clearly in error. The Court concluded that the trial judge had not abused her discretion when she refused to admit the plaintiff's expert testimony, because the claims of a causal connec- tion between the exposure and the injury made by the expert witness were too speculative. A third opinion issued in 1999, Kumho, dealt with inadmis- sibility of engineering testimony offered to prove defect and causation in a product-liability action. In this case, the plaintiffs claimed that the blowout of a defective tire on a minivan caused death and serious injuries. The plaintiffs relied on testimony by an expert in tire-failure analysis, who concluded that the tire must have been defective due to the absence of a number of indicia of abuse by the driver. The trial court concluded that the testimony satisfied none of the four Daubert criteria and excluded it, granting the defendants' motion for summary judgment. The appellate court reversed, ruling that the Daubert standards did not extend to such engineering evidence. The Supreme Court rejected this narrow application of Daubert and directed the courts to use flexible 5

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DISCUSSIONS OF THE COMMITTEE ON DAUBERT STANDARDS standards appropriate to different fields of expertise. The Kumho opinion contemplated that in some cases some expert witnesses may be permitted to testify based on expertise arising from their experience. The objective of Daubert's gatekeeping requirement said the Court "is to make certain that an expert, whether basing testimony upon professional studies or personal experience, employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field." In toxic tort cases, the plaintiff normally must show (1) plaintiff's exposure to a toxic substance for which the defendant is responsible; (2) exposure to the toxic substance is known to cause the type of injury suffered by the plaintiff (general causation); (3) the toxic substance did in fact cause the plaintiff's injury (specific causation); and (4) the extent of the injury to the plaintiff. Much of the proof for each of the above elements (and especially 2 and 3), must come in the form of expert testimony. Insistence on applying Daubert to each element of expert testimony means the plaintiff must make a detailed showing that the expert applies sound science every step of the way. When a trial judge excludes expert testimony, he or she preempts the opportunity for a jury to consider the issue at hand. If the judge excludes expert evidence that is essential to meeting a party's burden in a case, the judge will also grant a motion for summary judgment and terminate the litigation in favor of the opponent of the excluded expert testimony. This means that the case will not be heard by a jury. Under current law this is the correct outcome if a party is unable to present admissible evidence on an essential element of the case. 6