Assessing the fitness of novel scientific evidence in the post-Daubert era: pesticide exposure cases as a paradigm for determining admissibility.

• Author: Mahaney, Erin K.L.

1. INTRODUCTION

   Problems inhere with the introduction of scientific evidence to prove general and specific causation. In particular, novel scientific evidence proffered in toxic tort litigation presents considerable problems for courts today. Novel scientific evidence refers to evidence or theories that have not received approbation from the judicial or scientific communities.(1) Unproven scientific theories raise countervailing concerns that a liberal admission standard will impede the judicial process or that a restrictive standard will prevent courts from becoming fully informed about the latest scientific developments.(2) The U.S. Supreme Court addressed the admissibility of novel scientific evidence under Federal Rule of Evidence 702 in Daubert v. Merrell Dow Pharmaceuticals, Inc.(3) It elucidated a two-part test that requires a preliminary assessment of 1) the validity of the scientific knowledge in question, and 2) the "fit" between the proffered scientific evidence and the circumstances of the plaintiff's case.(4) The second prong of this test -- the fitness requirement -- demands a more specialized inquiry into the relevancy of proffered scientific evidence.

   While Rule 702's first requirement of scientific validity has been oft-discussed in case law and literature,(5) its fitness requirement has received far less attention. Nonetheless, the issue of fit warrants closer examination because it provides an important tool for the judge as gatekeeper. Not only must a theory be grounded upon reliable scientific knowledge, it also must be relevant to the facts of the case. Accordingly, when used in conjunction with Rule 702's first prong of scientific validity, the fitness requirement affords a valuable means of excluding "pseudoscientific assertions" without sanctioning a "stifling and repressive scientific orthodoxy [that] will be inimical to the search for truth."(6)

   Pesticide exposure cases offer a paradigm for exploring the issues raised by the application of Federal Rule of Evidence 702's fitness requirement to novel scientific theories in the toxic tort context. These exposure cases typify many of the problems associated with evaluating the admissibility of novel scientific theories and are representative of the difficulty of proving causation in toxic tort cases generally.(7) Primarily, exposure cases present the intrinsic difficulty of proving a link between pesticide exposure and disease where biological and physiological mechanisms are poorly understood and epidemiological evidence is scarce.(8) Accordingly, they afford a useful tool for examining the Daubert Court's interpretation of Rule 702 as it applies to novel scientific evidence. Further, it is important to consider these cases because pesticide exposure cases may represent "first cases"(9) that become more common as the Enviromental Protection Agency (EPA) reregisters pesticides, as scientific knowledge develops, or as "hot topics" arise, such as the controversial link between estrogenic chemicals and breast cancer.(10) Because pesticide exposure cases illustrate the difficulties in determining what is relevant evidence in cases involving novel scientific theories, they are a particularly apt vehicle for examining application of Rule 702's fitness test.

   This Article first examines the admissibility of expert testimony under Rule 702 and how the Daubert Court elucidated the fitness requirement. Next the Article reviews the post-Daubert application of Rule 702's fitness test and discusses what circumstances might trigger application of the test. Judicial interpretation and application of this test are then used to examine the potential admissibility of scientific evidence in pesticide exposure cases, assuming that the requirements of the first prong -- valid scientific knowledge -- have been met. Finally, results of this examination are extrapolated to cases involving novel scientific evidence, and suggestions are provided for analyzing this evidence under Rule 702's fitness test.

2. FEDERAL RULE OF EVIDENCE 702

   The complexity of scientific theories and evidence in toxic tort litigation often necessitates expert testimony that will assist the trier in making an intelligent evaluation of facts. Federal Rule of Evidence 702 provides for the admissibility of such testimony:

   If scientific, technical or other specialized knowledge will assist the

   trier of

   fact to understand the evidence or to determine a fact in issue, a witness

   qualified as an expert by knowledge, skill experience, training, or

   education, may

   testify thereto in the form of an opinion or otherwise.(11)

   The expert witness may explain the "scientific . . . principles relevant to the case, leaving the trier of fact to apply them to the facts," or the expert may "take the further step of suggest the inference which should be drawn from apply the specialized knowledge to the facts."(12) The trier of fact's implicit unfamiliarity with the relevant scientific principles raises concerns regarding potential abuse of this Rule.(13) For example, scientific expert testimony could be used to mislead the trier, or it could be used as a trial technique to wear down adversaries.(14) Further, admission of meritless scientific testimony wastes judicial resources that could be better spent resolving other issues.(15) The U.S. Supreme Court addressed these concerns, in part, in Daubert v. Merrell Dow Pharmaceuticals, Inc.(16)

   In Daubert, the plaintiffs sued a pharmaceutical company to recover for birth defects allegedly caused by the mother's ingestion of Bendectin, a prescription anti-nausea drug.(17) The defendant moved for summary judgment, contending that the vast amount of epidemiological data available failed to show that Bendectin created a risk factor for birth defects.(18) Consequently, the defendant argued, the plaintiffs would be unable to provide admissible evidence to the contrary.(19) The plaintiffs responded with the testimony of eight experts who concluded that Bendectin could cause birth defects. The experts based their conclusions upon in vitro (whole, live animal) and in vivo (animal cell) studies, pharmacological studies of the drug's chemical structure, and reanalysis of previously published epidemiological studies.(20) The district and appellate courts, relying upon the "general acceptance" test established in Frye v. United States,(21) both determined that the plaintiffs' evidence was inadmissible because the studies relied upon by the plaintiffs' experts were not generally accepted in the field.(22) The Supreme Court granted certiorari "in light of sharp divisions among the courts regarding the proper standard for the admission of expert testimony."(23)

   In Daubert, the Court held that the Federal Rules of Evidence furnish the standard for determining the admissibility of novel scientific evidence, thus superseding Foe.(24) The Court established Rule 702 as the "primary locus" of the federal judiciary's gatekeeping role in determining the admissibility of proffered expert testimony.(25) The Court located within Rule 702 a two-part test for determining the admissibility of expert testimony.(26) The first prong of the test requires the trier of fact to ascertain whether the expert's testimony pertains to validated scientific knowledge, thus establishing "a standard of evidentiary reliability."(27) The second prong of the test requires an assessment of whether the "reasoning or methodology properly can be applied to the facts in issue," thus establishing the relevancy of the testimony.(28) Evidence that is not relevant will not "assist the trier of fact to understand the evidence or to determine a fact in issue" and is inadmissible.(29) The Court characterized this facet of Rule 702 as one of fit -- the expert testimony proffered in the case must be sufficiently tied to the facts of the case so that "`it will aid the jury in resolving a factual dispute.'"30 Hence, this fitness requirement "requires a valid scientific connection to the pertinent inquiry as a precondition to admissibility."(31)

   The Court offered little guidance for determining fit in cases involving novel scientific theories. Although the Court noted that Rule 702 does not "apply specially or exclusively to unconventional evidence," it conceded that well-established propositions are less likely to be challenged, and are thus more easily defended under Rule 702.(32) It recognized that "`fit' is not always obvious, and scientific validity for one purpose is not necessarily scientific validity for other, unrelated purposes."(33) Justice Blackmun, writing for the majority opinion, noted:

   The study of the phases of the moon, for example, may provide valid scientific

   "knowledge" about whether a certain right was dark, and if darkness is a fact

   in issue, the knowledge will assist the trier of fact. However (absent creditable

   grounds supporting such a link), evidence that the moon was full on a certain

   night will not assist the trier of fact in determining whether an individual was

   unusually likely to have behaved irrationally on that night.(34)

   The Court's "phases of the moon" example posits an obvious instance in which there is no scientific connection to the fact in issue. However, as the Ninth Circuit noted upon remand, "[t]he task before us is more daunting still when the dispute concerns matters at the very cutting edge of scientific research, where fact meets theory and certainty dissolves into probability."(35)

3. Post-Daubert Application of Rule 702

   Before determining the admissibility of scientific evidence in pesticide exposure cases, it is helpful to explore the analysis required under the second prong of Rule 702. In general, post-Daubert case law provides little guidance. A review of federal cases reveals that few courts have reached the second prong of the Rule 702 admissibility test. Many courts that have conducted a Rule 702 analysis ended their inquiry with a determination that the first...