Judicial Boundary Drawing and the Need for Context-Sensitive Science in Toxic Torts after Daubert v. Merrell Dow Pharmaceutical Inc.
By Carl F. Cranor, John G. Fischer, and David A. Eastmond
INTRODUCTION
What admissibility standards should govern the introduction of scientific evidence in toxic tort litigation? In many toxic tort cases, the only evidence available to prove that the toxic substance at issue caused the plaintiff's injury is scientific opinion testimony; thus, its introduction or exclusion may determine the outcome of the case. This question has remained open since the U.S. Supreme Court addressed this issue over three years ago, when it enunciated a new test for the admissibility of scientific evidence. The Supreme Court, in Daubert v. Merrell Dow Pharmaceuticals, Inc., rejected the Frye test for the admissibility of scientific evidence in toxic tort cases, holding that it had been superseded by the Federal Rules of Evidence. The Court wrote: “[I]n order to qualify as ‘scientific knowledge,’ an inference or assertion must be derived by the scientific method. Proposed testimony must be supported by appropriate validation--i.e., ‘good grounds,’ based on what is known.” It further held that “Rule 702 . . . contemplates some degree of regulation of the subjects and theories about which an expert may testify.” Thus, a trial judge “must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable.” Moreover, there must be a “grounding in the methods and procedures of science,” the knowledge “must be derived by the scientific method,” and the knowledge must be “relevant” to the facts of the case. A ruling on admissibility thus entails a preliminary assessment “of whether the reasoning or methodology underlying the testimony is scientifically valid and of whether that reasoning or methodology properly can be applied to the facts in issue.”
In light of the Daubert decision, this article addresses the issue of the use of scientific evidence in civil litigation, using the science required in toxic tort cases as an example. We aim not so much to provide an interpretation of the Daubert decision, but to address several substantive issues that the decision and subsequent interpretations raise about the role of scientific testimony in toxic tort litigation. The Court has now officially given judges a “gate-keeping” role in admitting scientific evidence which explicitly authorizes them to draw “boundaries” around what may be admitted as scientific evidence for tort law purposes. This is a power, however, that must be used sensitively and subtly to serve well the parties to tort litigation; this article seeks to provide some guidance as to how this power should be exercised.
When engaging in “boundary drawing,” judges risk at least two generic mistakes: explanatory mistakes and strength mistakes. Judges make explanatory mistakes when they impose improper substantive restrictions on the content of evidence that may be admitted to prove that a substance causes human harm. For *4 instance, a judge might insist that a party provide either a particular kind of evidence, such as epidemiological studies, or multiple kinds of evidence, such as epidemiological, animal, and mechanistic evidence. Such restrictions would be mistakes because any appropriate scientific evidence that helps to explain the causal relationship between a defendant's actions and a plaintiff's injury is relevant and should be admissible. There are a variety of different explanatory paths that may lead to a conclusion; no particular explanation should be precluded as long as it has appropriate support. Moreover, many different legitimate scientists and scientific disciplines can contribute evidence in support of an explanation that a defendant more probably than not has harmed a plaintiff. Thus, as we discuss below, various proposed content restrictions on scientific explanations should be avoided.
A second generic problem is to mistake the strength of evidence required for a firm scientific conclusion that a substance causes human harm with the strength of evidence needed for a tort law conclusion. Tort law and scientific inquiry are different institutions, each with different evidentiary and social goals. A judge's failure to be sensitive to these differences when admitting scientific evidence in tort cases may inadvertently distort the law. We are concerned that judges may accept only certain kinds of scientific answers, given by certain kinds of scientists, to questions that are fundamentally legal in nature. In particular, judges might effectively change tort law standards of evidence, replacing them with scientific evidence standards more stringent than those that many respectable scientists would adopt. Judges should avoid this potential error, and should keep distinct the goals, mandates, and standards of tort law and science, in order to avoid mistaken admissibility decisions that may inadvertently change the desirable balance of interests between adversaries in tort litigation.
To address these concerns, we argue that courts should adopt admissibility rules that are sufficiently sensitive to allow the admissibility of all the evidence upon which scientists routinely rely to draw conclusions about harm from toxic substances. In this endeavor, courts should adhere to notions of admissibility in tort cases that reflect the goals and aims of tort law. Finally, courts must maintain a fair balance of procedural and substantive interests between plaintiffs and defendants.
This article suggests considerations and standards for admissibility that attempt to balance the sometimes inconsistent goals of tort law and science. To introduce this discussion, in Section II we characterize the effect of the Daubert decision. Following a brief discussion of the facts of the case, we present and critique various views on the effect of the substance of Daubert. Those views advocate a range of interpretations, from overly liberalizing to stringently curtailing admissibility rules. In addition, we identify three procedural concerns raised by the decision which should similarly inform future admissibility decisions. In Section III, we then analyze some of the dangers posed by some types of admissibility rules offered in response to Daubert. In this section, we begin with the basic premise that evidentiary requirements for tort law and for scientific purposes are somewhat different. If these differences are not acknowledged by the courts they will inadvertently change the law. In addition to neglecting the epistemological contexts of tort law and scientific practice, courts may ignore the complexity of decisions made by scientists in their research. Such an approach risks the promulgation of “cookbook” admissibility rules--evidentiary rules that may appear as easy to use as the recipes in a cookbook--and the use of “cookbook” scientific evidence. That is, when courts are faced with the daunting task of evaluating the validity of scientific evidence, as Daubert commands, they may well develop, to change the metaphor, overly simple, “bright-line” criteria for the admissibility of scientific evidence that may be inappropriate in the tort law process. In this discussion, we identify and critique examples of such overly stringent admissibility rules. We then present a number of policy arguments against adopting such overly stringent rules in the tort law context. Finally, Section IV sketches an alternative view of how scientific evidence in toxic tort litigation might be addressed by the courts, focussing primarily on the use of animal studies, a particularly controversial area.
Generally, we feel the new focus on science after Daubert is salutary. However, because there is little guidance as to what constitutes admissible scientific evidence, there is a risk of erroneous application of the Daubert commands. On the one hand, courts risk excluding too much evidence. They must be more thoroughgoing in their acceptance of the wide range of scientific evidence--evidence routinely relied upon by the scientific community for arriving at scientific judgments. On the other hand, courts should be more sensitive to the mistakes that can arise from overly-simple views of scientific evidence--bright-line rules and overly-stringent evidentiary standards adopted from some understandings of science--and to the use of this evidentiary material in tort law. Ultimately, judges and lawyers may need to experience a quantum leap in understanding the subtleties of scientific inquiry in order to prevent various simplified views of scientific evidence from undermining and subverting the goals of tort law.
What admissibility standards should govern the introduction of scientific evidence in toxic tort litigation? In many toxic tort cases, the only evidence available to prove that the toxic substance at issue caused the plaintiff's injury is scientific opinion testimony; thus, its introduction or exclusion may determine the outcome of the case. This question has remained open since the U.S. Supreme Court addressed this issue over three years ago, when it enunciated a new test for the admissibility of scientific evidence. The Supreme Court, in Daubert v. Merrell Dow Pharmaceuticals, Inc., rejected the Frye test for the admissibility of scientific evidence in toxic tort cases, holding that it had been superseded by the Federal Rules of Evidence. The Court wrote: “[I]n order to qualify as ‘scientific knowledge,’ an inference or assertion must be derived by the scientific method. Proposed testimony must be supported by appropriate validation--i.e., ‘good grounds,’ based on what is known.” It further held that “Rule 702 . . . contemplates some degree of regulation of the subjects and theories about which an expert may testify.” Thus, a trial judge “must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable.” Moreover, there must be a “grounding in the methods and procedures of science,” the knowledge “must be derived by the scientific method,” and the knowledge must be “relevant” to the facts of the case. A ruling on admissibility thus entails a preliminary assessment “of whether the reasoning or methodology underlying the testimony is scientifically valid and of whether that reasoning or methodology properly can be applied to the facts in issue.”
In light of the Daubert decision, this article addresses the issue of the use of scientific evidence in civil litigation, using the science required in toxic tort cases as an example. We aim not so much to provide an interpretation of the Daubert decision, but to address several substantive issues that the decision and subsequent interpretations raise about the role of scientific testimony in toxic tort litigation. The Court has now officially given judges a “gate-keeping” role in admitting scientific evidence which explicitly authorizes them to draw “boundaries” around what may be admitted as scientific evidence for tort law purposes. This is a power, however, that must be used sensitively and subtly to serve well the parties to tort litigation; this article seeks to provide some guidance as to how this power should be exercised.
When engaging in “boundary drawing,” judges risk at least two generic mistakes: explanatory mistakes and strength mistakes. Judges make explanatory mistakes when they impose improper substantive restrictions on the content of evidence that may be admitted to prove that a substance causes human harm. For *4 instance, a judge might insist that a party provide either a particular kind of evidence, such as epidemiological studies, or multiple kinds of evidence, such as epidemiological, animal, and mechanistic evidence. Such restrictions would be mistakes because any appropriate scientific evidence that helps to explain the causal relationship between a defendant's actions and a plaintiff's injury is relevant and should be admissible. There are a variety of different explanatory paths that may lead to a conclusion; no particular explanation should be precluded as long as it has appropriate support. Moreover, many different legitimate scientists and scientific disciplines can contribute evidence in support of an explanation that a defendant more probably than not has harmed a plaintiff. Thus, as we discuss below, various proposed content restrictions on scientific explanations should be avoided.
A second generic problem is to mistake the strength of evidence required for a firm scientific conclusion that a substance causes human harm with the strength of evidence needed for a tort law conclusion. Tort law and scientific inquiry are different institutions, each with different evidentiary and social goals. A judge's failure to be sensitive to these differences when admitting scientific evidence in tort cases may inadvertently distort the law. We are concerned that judges may accept only certain kinds of scientific answers, given by certain kinds of scientists, to questions that are fundamentally legal in nature. In particular, judges might effectively change tort law standards of evidence, replacing them with scientific evidence standards more stringent than those that many respectable scientists would adopt. Judges should avoid this potential error, and should keep distinct the goals, mandates, and standards of tort law and science, in order to avoid mistaken admissibility decisions that may inadvertently change the desirable balance of interests between adversaries in tort litigation.
To address these concerns, we argue that courts should adopt admissibility rules that are sufficiently sensitive to allow the admissibility of all the evidence upon which scientists routinely rely to draw conclusions about harm from toxic substances. In this endeavor, courts should adhere to notions of admissibility in tort cases that reflect the goals and aims of tort law. Finally, courts must maintain a fair balance of procedural and substantive interests between plaintiffs and defendants.
This article suggests considerations and standards for admissibility that attempt to balance the sometimes inconsistent goals of tort law and science. To introduce this discussion, in Section II we characterize the effect of the Daubert decision. Following a brief discussion of the facts of the case, we present and critique various views on the effect of the substance of Daubert. Those views advocate a range of interpretations, from overly liberalizing to stringently curtailing admissibility rules. In addition, we identify three procedural concerns raised by the decision which should similarly inform future admissibility decisions. In Section III, we then analyze some of the dangers posed by some types of admissibility rules offered in response to Daubert. In this section, we begin with the basic premise that evidentiary requirements for tort law and for scientific purposes are somewhat different. If these differences are not acknowledged by the courts they will inadvertently change the law. In addition to neglecting the epistemological contexts of tort law and scientific practice, courts may ignore the complexity of decisions made by scientists in their research. Such an approach risks the promulgation of “cookbook” admissibility rules--evidentiary rules that may appear as easy to use as the recipes in a cookbook--and the use of “cookbook” scientific evidence. That is, when courts are faced with the daunting task of evaluating the validity of scientific evidence, as Daubert commands, they may well develop, to change the metaphor, overly simple, “bright-line” criteria for the admissibility of scientific evidence that may be inappropriate in the tort law process. In this discussion, we identify and critique examples of such overly stringent admissibility rules. We then present a number of policy arguments against adopting such overly stringent rules in the tort law context. Finally, Section IV sketches an alternative view of how scientific evidence in toxic tort litigation might be addressed by the courts, focussing primarily on the use of animal studies, a particularly controversial area.
Generally, we feel the new focus on science after Daubert is salutary. However, because there is little guidance as to what constitutes admissible scientific evidence, there is a risk of erroneous application of the Daubert commands. On the one hand, courts risk excluding too much evidence. They must be more thoroughgoing in their acceptance of the wide range of scientific evidence--evidence routinely relied upon by the scientific community for arriving at scientific judgments. On the other hand, courts should be more sensitive to the mistakes that can arise from overly-simple views of scientific evidence--bright-line rules and overly-stringent evidentiary standards adopted from some understandings of science--and to the use of this evidentiary material in tort law. Ultimately, judges and lawyers may need to experience a quantum leap in understanding the subtleties of scientific inquiry in order to prevent various simplified views of scientific evidence from undermining and subverting the goals of tort law.
