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Introduction

“In this age of science, we must build legal foundations that are sound in science as well as in law. Scientists have offered their help. We in the legal community should accept that offer. We are in the process of doing so.”

—Associate Justice Stephen Breyer “Introduction” in Reference Manual on Scientific Evidence, Second Edition (Federal Judicial Center, 2000)

As society has come increasingly to depend on science and technology, more scientists, engineers, and physicians are asked to testify in courts of law on technical questions in their fields of expertise. They may be asked to provide facts in some cases and opinions in others, but their presence as “expert witnesses” has become familiar in cases dealing with disputed issues in tissue testing (do the blood samples match?), toxicology (does a certain chemical cause chromosomal abnormalities?), epidemiology (is another chemical associated with increased incidence of lung cancer?), engineering (why did a certain device fail?), and other subjects of technical complexity.

Scientists and other technical experts may be asked to testify in several kinds of civil litigation. These include product liability litigation, toxic tort cases, medical malpractice suits, and challenges to regulations that question the adequacy of the scientific underpinning of an adminis-trative case decision or regulation issued by a regulatory agency. There are also occasional opportunities for court review of agency decisions in some cases. Such decisions are generally subject to three types of inter-



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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop 1 Introduction “In this age of science, we must build legal foundations that are sound in science as well as in law. Scientists have offered their help. We in the legal community should accept that offer. We are in the process of doing so.” —Associate Justice Stephen Breyer “Introduction” in Reference Manual on Scientific Evidence, Second Edition (Federal Judicial Center, 2000) As society has come increasingly to depend on science and technology, more scientists, engineers, and physicians are asked to testify in courts of law on technical questions in their fields of expertise. They may be asked to provide facts in some cases and opinions in others, but their presence as “expert witnesses” has become familiar in cases dealing with disputed issues in tissue testing (do the blood samples match?), toxicology (does a certain chemical cause chromosomal abnormalities?), epidemiology (is another chemical associated with increased incidence of lung cancer?), engineering (why did a certain device fail?), and other subjects of technical complexity. Scientists and other technical experts may be asked to testify in several kinds of civil litigation. These include product liability litigation, toxic tort cases, medical malpractice suits, and challenges to regulations that question the adequacy of the scientific underpinning of an adminis-trative case decision or regulation issued by a regulatory agency. There are also occasional opportunities for court review of agency decisions in some cases. Such decisions are generally subject to three types of inter-

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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop related tests: (1) the statutory wording that governs the level of scientific or engineering certainty about toxicity or product risk; (2) the specific level of protectiveness required (e.g., “ample margin of safety” or the absence of “unreasonable risk”); and (3) whether the findings are governed by a legal test of deference to an agency decision (“preponderance of the evidence” vs. “arbitrary and capricious”).1 The courts apply no single level of rigor for the science or other expertise used as evidence in civil litigation. The rigor applied by the court may vary as a function of the jurisdiction of the court (federal, state, adminis-trative law judge whether the case is governed by common law or statute) and of the stakes involved. Higher stakes (e.g., major injuries, massive recalls) sometimes appear to require more evidence and a higher level of proof of causation. In addition, juries may be more skeptical of evidence if a verdict will result in an enormous award or threaten the viability of a major institution. The rigor of scientific evidence may vary with the purpose of the inquiry; a lower level of rigor may be required to simply list a substance as “toxic” for reporting purposes (e.g., for the Toxic Release Inventory), a higher level to impose regulatory restrictions, an even higher level to award huge damages, and a higher level still to ban a substance from use.2 One arena that has proven especially troublesome for courts is the question of causation in so-called toxic tort cases, which might be considered as a subspecies of product liability litigation.3 Because many of these cases turn on points of technical complexity, expert witnesses are often required to provide testimony. Much is at stake—the viability of firms or whole industries, the ability for injured parties to receive ade-quate compensation, and costly litigation burdens and settlement sums. Therefore, courts have tried hard to improve their standards for admitting and weighing scientific and technical evidence. 1   See, e.g., Chevron U.S.A., Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837 (1984), Christensen v. Harris County, 529 U.S. 576 (2000) . See also Ernest Gellhorn & Paul Verkuil, Controlling Chevron-Based Delegations, 20 Cardozo L. Rev. 989 (1999), U.S. v. Mead Corp., 533 U.S. (2001). 2   There are also important distinctions among rigor (the reliability of evidence), accuracy (test variability), and precision (the level of accuracy to which a test can measure). 3   The prevalence of toxic tort litigation, which seeks to resolve claims by individuals that they have been injured by exposure to chemicals or other products, has grown rapidly in recent years, amid considerable controversy. Some people criticize toxic tort litigants for seeking to impose liability for exposures that carry little or no risk to individuals (e.g., air pollution), especially when compared to other, larger risks under a person’s voluntary control (e.g., driving, smoking). The law reflects this distinction, however, and finds relatively low risks that are involuntary to be actionable or sufficient to warrant regulation.

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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop The resolution of toxic tort cases may affect large classes of people or ways of performing critical functions. As Justice Breyer has pointed out, “[M]odern life, including good health as well as economic well-being, depends upon the use of artificial or manufactured substances, such as chemicals. And it may, therefore, prove particularly important to see that judges . . . help assure that the powerful engine of tort liability, which can generate strong financial incentives to reduce, or to eliminate, production, points towards the right substances and does not destroy the wrong ones. It is, thus, essential in this science-related area that the courts administer the Federal Rules of Evidence in order to achieve the ‘end[s]’ that the Rules themselves set forth, not only so that proceedings may be ‘justly determined,’ but also so ‘that the truth may be ascertained.’ ” 4 At the same time, many scientific, engineering, and medical experts who have been asked to testify in the courtroom have experienced tension and occasionally frustration. Some feel that they are unable to communicate their knowledge in sufficient detail to nonscientists; others find their evidence, their expertise, and even their careers under attack. Another cause of experts’ frustration transcends the high stakes of litigation. The role of scientists in the courtroom turns out, as one would expect, to differ in significant respects from their role in the laboratory. For example, in the courtroom, scientists are often asked for a yes-or-no answer to a question in which they discern shades of gray. In addition, inherent differences between the cultures of law and science are magni-fied under courtroom conditions, especially in the context of cross-exami-nation. There is anecdotal evidence that these differences may dissuade scientists and engineers from stepping forward in cases where the nation needs the benefit of their expertise. BRINGING LAWYERS AND SCIENTISTS TOGETHER For these and other reasons, the National Academies, in their role representing the scientific, engineering, and medical communities, have taken a strong interest in the preparation, presentation, and handling of expert testimony. That interest crystallized several years ago when the case Daubert v. Merrell Dow Pharmaceuticals, Inc. reached the Supreme Court.5 The National Academies were moved to join with the American Association for the Advancement of Science (AAAS) to file an amici curiae brief in a case that has done much to update the role of scientific expert 4   General Electric Co. v. Joiner, 118 S.Ct. 512, 520 (1997) (J. Breyer, concurring), citing Fed. Rule. Evid. 102. 5   Daubert v. Merrell Dow Pharmaceuticals, Inc., 113 S. Ct. 2786 (1993).

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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop witnesses and the admissibility of scientific evidence. The Court largely adopted the argument of the brief that scientific evidence should be evalu-ated by the standards of the scientific community. Justice Blackmun noted that “there are no certainties in science” and quoted the AAAS/NAS amici brief : “Science is not an encyclopedic body of knowledge about the universe. Instead, it represents a process for proposing and refining theo-retical explanations about the world that are subject to further testing and refinement.”6 One of the outcomes of Daubert (pronounced Dow-bert) is that judges have considerable responsibility in understanding and acting on questions of scientific complexity that may have their roots in such fields as epidemiology, toxicology, and molecular genetics. To fulfill this responsibility, judges—at least federal trial judges—are asked to serve a “gatekeeping” role in deciding whether the expert testimony is sufficiently reliable to be presented at trial. In doing so, judges, few of whom have technical training, are asked to exercise a degree of expertise themselves in grappling with cause-and-effect issues on which scientific experts themselves may disagree. Of equal concern are the differences in language and culture between science and law that are heightened in the courtroom. In order to survey the difficulties produced by this considerable responsibility, the Science, Technology, and Law Program of the National Academies invited individuals from the legal, scientific, and engineering communities, most of whom had considerable experience with expert testimony, to a day-long workshop to seek a full range of opinions. The workshop was not intended to seek a consensus. Instead it sought to air differences and explore emerging problems. In order to achieve this purpose, the National Academies invited experts representing a broad spectrum of opinion as to what level of scientific validation should be required to be admitted as evidence in civil cases. The following summary attempts to capture the main points of the day’s discussion. While such a brief summary necessarily omits much, its purpose is to illuminate the main features of the landscape in which scientists and lawyers find themselves in light of Daubert and the challenge of identifying objective and unbiased scientific experts for court-appointed roles. Among those features are the nature of expert evidence, the rules of evidence as applied to science, the scientific method and its application in law, and the many difficulties in reaching conclusions about causation when experts disagree. 6   Brief for the American Association for the Advancement of Science and the National Academy of Sciences as Amici-Curiae 7-8.