At Law: Facts, Values, and Expert Testimony

Abstract

In a court of law, we ordinary mortals are usually confined to testifying about matters of which we have direct - things we have personally seen or heard. Not so expert witnesses, who are permitted to offer their opinions. Successful expert witnesses who combine impressive credentials with die ability to charm their listeners may in effect take over a jury's function, since their opinions may extend to the ultimate in a case, such as whether die defendant was negligent. Experts can have unusual influence when novel science is at issue, as is sometimes true in cases of interest to bioethicists - for instance, the genetics of homosexuality, the biological status of frozen human zygotes or embryos, the effects of psychosurgery, or the reliability of genetic fingerprints. When a dispute lies at the heart of the question, What probably happened; an expert's opinion is often crucial in determining whether the case will even go to trial. Such, indeed, was the result in a case filed by two children born with serious birth defects and their parents against the company that marketed Bendectin, a prescription anti-nausea drug that the children's mothers took while pregnant. Having reviewed the thirty relevant published studies involving over 130,000 patients, a physician-epidemiologist who served as an expert for the defendant concluded maternal use of Bendectin during the first trimester has not been shown to be a risk factor for human birth defects.[1] Instead of challenging this expert's characterization of the literature, the plaintiffs in Daubert v. Merrell Dow attempted to refute his conclusion by providing eight other experts' affidavits based on in vitro and animal studies, the similarity in chemical structure of Bendectin to other known teratogens, and a reanalysis of the published epidemiologic studies. In light of the vast extent of those studies, the federal district judge ruled that expert testimony regarding causation would be limited to epidemiologic data, but the statistical recalculations would not be admitted because they had not been published or subjected to peer review. Precluded from introducing their expert testimony, the plaintiffs had no case, and the trial judge granted the defendant's motion for summary judgment. The court of appeals affirmed on the basis that the unpublished reanalyses did not meet the requirement set forth in Frye v. United States that a technique be generally accepted as reliable in the relevant community.[2] On 28 June 1993, the United States Supreme Court reversed the appellate court and sent the case back for further proceedings. Most of justice Blackmun's opinion (parts of which were for a unanimous court, while other parts were for everyone except Chief justice Rehnquist, who dissented, and justice Stevens, who joined him) is of interest only to lawyers, but buried among technical points about the law of lies an important issue of values, to which we will turn in a moment. The Court rejected the Frye test, which for seventy years had set the standard for admission of evidence, not because it found fault with its general acceptance rule (though that rule has had many detractors over the years) but because the Court concluded that Congress, in adopting the Federal Rules of Evidence twenty years ago, chose not to incorporate Frye into them. Rule 402 sets a very liberal standard in favor of admission of all relevant evidence (not excluded by another rule). Because expert testimony can be both powerful and misleading, the Court in Daubert construes the rule on admission of expert evidence, Rule 702, to require that the theories and techniques about which an expert proposes to testify be reliable. The majority derives this from what commentators call the helpfulness criterion, based on Rule 702's provision that expert testimony regarding scientific knowledge is allowed when it will assist the trier of fact. …