Assessing the Fitness of Novel Scientific Evidence in the Post-Daubert Era: Pesticide Exposure Cases as a Paradigm for Determining Admissibility

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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. …