3
The Nature of Expert Evidence

“My favorite novelist is Trollope. He was once a fact witness in a court case. The cross-examination was something like the following: ‘Now Mr. Trollope, you’re the author of 38 books, aren’t you?’ ‘Yes.’ ‘And there isn’t a word of truth in any of them, is there? ’ ”

— David Freedman

As the number of legal cases raising complex scientific and technical issues has increased, along with the financial consequences to individuals and businesses, courts have struggled to find a clear standard by which to admit expert evidence. Some critics have attempted to begin by posing the existence of a line between science and “junk” science. Claims that junk science has infected the nation’s courtrooms are common, even though few people agree on a definition for the term. One participant suggested that “junk” is a general term used to describe evidence that favors plaintiffs in product liability or toxic tort litigation. Another suggested that the term was sometimes applied to scientists employed or funded by corporations and who testify on behalf of those corporations. More broadly, however, the existence of the term reflects some confusion and even cynicism on the part of both expert witnesses and lawyers about the value and objectivity of evidence.

Making expert evidence comprehensible to laypeople serving on juries constitutes a significant challenge to the court, argued one participant. Current trial procedures, he said, have arisen from a need to resolve



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 10
The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop 3 The Nature of Expert Evidence “My favorite novelist is Trollope. He was once a fact witness in a court case. The cross-examination was something like the following: ‘Now Mr. Trollope, you’re the author of 38 books, aren’t you?’ ‘Yes.’ ‘And there isn’t a word of truth in any of them, is there? ’ ” — David Freedman As the number of legal cases raising complex scientific and technical issues has increased, along with the financial consequences to individuals and businesses, courts have struggled to find a clear standard by which to admit expert evidence. Some critics have attempted to begin by posing the existence of a line between science and “junk” science. Claims that junk science has infected the nation’s courtrooms are common, even though few people agree on a definition for the term. One participant suggested that “junk” is a general term used to describe evidence that favors plaintiffs in product liability or toxic tort litigation. Another suggested that the term was sometimes applied to scientists employed or funded by corporations and who testify on behalf of those corporations. More broadly, however, the existence of the term reflects some confusion and even cynicism on the part of both expert witnesses and lawyers about the value and objectivity of evidence. Making expert evidence comprehensible to laypeople serving on juries constitutes a significant challenge to the court, argued one participant. Current trial procedures, he said, have arisen from a need to resolve

OCR for page 10
The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop conventional disputes of all kinds, most of which have little or no “technical” content. In general, a trial is an educational and inferential process in which evidence is heard, weighed against other evidence, and applied to the circumstances of the case to determine a verdict. Admitting scientific and other expert evidence that is unfamiliar to the average juror presents a fundamental shift in this paradigm, stated one participant. Further, noted the participant, there is a sharp difference between “conventional” evidence, to which non-experts on a jury may add personal life experiences that aid them in deliberations, and more specialized scientific evidence that “can only be deferred to.” One danger seen by this participant is that judges, knowing that jurors may defer to evidence or opinions they do not understand, may be excessively rigorous in excluding expert evidence in order to “protect” jurors. THE INCOMPLETE NATURE OF EVIDENCE As much as courts would like to winnow out unsound evidence, however, the task is not an easy one. As one lawyer emphasized, “all evidence is incomplete, and it’s always going to be.” To require absolute reliability in evidence is to expect an elusive and “non-existent purity in science” where virtually all scientific data might fail the most rigorous tests of reliability and relevance in some degree. This may be inherently unfair to whoever has the burden of proof. In toxic tort cases, the plaintiff has the burden of proof, and a court may question the fairness of asking a plaintiff to suffer because of scientific uncertainty. The lawyer added that virtually all scientific data might fail the most rigorous tests of “reliability” and “relevance” in some way. From a scientific standpoint, it should be apparent that a legal structure that requires the defendant to prove a negative would also be problematic. Other participants discussed the understandable desire on the part of courts for certainty and “bright lines” by which to decide on the admissibility of evidence. They said it is unfair to require a higher standard of accuracy from expert witnesses in the courtroom than exists in the world of science. Other participants noted that it is unfair to admit evidence that would not stand up to the scrutiny of the scientific community. WHAT CAUSES AN ABSENCE OF SCIENTIFIC DATA Courts may lack sufficient knowledge about a given chemical, disease agent, or other issue. The presence or absence of a valid scientific study may by itself determine a verdict in the courtroom. One scientist described a “decision tree” by which to explore the factors that motivate groups to fund certain studies and not others.

OCR for page 10
The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop In epidemiology, for example, the court must often answer the question, Has an association been demonstrated between a certain chemical and human injury? There are two possible answers. If the answer is yes, the court might decide to compensate the plaintiff. If the answer is no, the question is, Why not? Again, there are two possible answers: either a study has been done and it shows no association, or a study has not been done. If a study has not been done, the question again is, Why not? Again there are two possibilities: one, a study may not be feasible because of the current state of technology, the availability of funding, or other reasons; or, two, the study could have been done, but it has not. If such a study is not feasible, the court may ask whether it is fair to expect a plaintiff to suffer in the absence of scientific knowledge and the court may decide to compensate. On the other hand, one could argue that a defendant should not have to pay compensation if there is no sufficient evidence. The court may ask a defendant why such a study was not conducted. If a study has not been done that could have been, perhaps there is a mechanism to do the study now. This decision tree was offered as a basis for discussion. It also served to remind the workshop participants of how many factors influence the availability of sound evidence. CAN THE JUDGE AND JURY BE EXPECTED TO UNDERSTAND SCIENTIFIC EVIDENCE? The Daubert trilogy sets high expectations for the ability of trial judges to weigh the evidence of experts. A judge at the workshop summarized the responsibilities of the trial judge who is faced with admitting or rejecting scientific testimony. Under Rule 702, which governs admissibility, the trial judge must make a preliminary assessment of whether the testimony’s underlying reasoning and methodology are scientifically valid and can be applied to the facts at issue. The judge may consider whether the theory or technique in question can be (or has been) tested, whether it has been subjected to peer review and publication, its known or potential error rate, the existence and maintenance of standards controlling its operation, and whether it has attracted widespread acceptance within a relevant scientific community. A district judge has great discretion in determining admissibility of scientific evidence. The consequences of excluding scientific evidence at the trial court level can be great, noted a judge. If the judge should exclude critical scientific testimony and then enter summary judgment (i.e., deliver a decision without a jury trial) against the plaintiff on the

OCR for page 10
The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop grounds of lack of evidence, then that judgment would be given great deference by a court of appeals.10 BETTER EQUIPPING COURTS TO UNDERSTAND SCIENCE A participant suggested several ways to assist judges and jurors in dealing with expert evidence: (1) Experts could be required to produce detailed, written reports, as described (but sometimes not honored) in the new Rule 26(a) of the Federal Rules of Civil Procedure. These reports could be read and digested more carefully than oral testimony, which may be delivered in ambiguous language; (2) judges could explain clearly to jurors the existence of any biases among experts who were providing testimony;11 (3) juries and judges could be provided with better tools to evaluate expert testimony. At present, he said, jurors often get a “pitiful standard jury instruction which basically tells them that you can evaluate experts based on how confident they seemed of their views.” Instead, he advocated a more explicit discussion of some of the criteria that underlie good science. Juries, thus equipped, could then “. . . wrestle more fully with this very elusive, but very human enterprise that we call science.” Another participant suggested more organized programs to help judges and juries deal with the demands of Daubert.12 Steps that might be helpful include improving the educational tools provided to judges, developing model jury instructions, studying jury understanding of technical 10   Note that in his decision on Joiner, Chief Justice Rehnquist wrote that the Court of Appeals erred in its review of the exclusion of Joiner’s experts’ testimony, and wrote: “In applying an overly ‘stringent’ review to that ruling, it failed to give the trial court the deference that is the hallmark of abuse of discretion review.” 11   The potential for bias may be obvious in cases where a witness is an employee of the defendant, or paid by the defendant. But even witnesses who do not have a pecuniary stake in the outcome may want to bolster a pet theory, attack big business for personal reasons, or create an incentive for more research in which they may play a part. It is not unreasonable to suspect bias in someone who always testifies for the defense or always testifies for the plaintiff in toxic tort cases, regardless of the financial situation. Under existing law the parties are free to explore these issues both through cross-examination of an expert and by extrinsic proof. 12   There are several programs providing judges with additional assistance: (1)The Court Appointed Scientific Experts (CASE) demonstration project, launched by the AAAS, helps judges identify qualified scientists and engineers to serve as experts to the court; (2) The Private Adjudication Center, Inc., of Duke University School of Law also maintains a regis-try of independent scientific and technical experts who are willing to provide advice to courts or serve as court-appointed experts; and (3) The Federal Judicial Center, the National Center for State Courts, and the National Judicial College offer programs to acquaint judges with scientific principles and evidentiary standards used to evaluate the admissibility of technical proof.

OCR for page 10
The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop evidence, and developing standards for expert witnesses. The last step, noted the participant, is controversial on the grounds that standardiza-tion might not be desirable or possible among the varying disciplines of science. A substantial debate was raised over the question of whether juries are asked to do too much in trials of technical complexity, such as patent cases. A judge argued strongly in favor of keeping juries for all trials. “Juries are the bedrock of the system,” he said. Rather than replacing juries, he suggested that the responsibility for making trials comprehensible to jurors rests with the judge. “We must make the work of the jurors more doable,” he said.