The U.S. Supreme Court's 1993 Daubert decision clarified the standards that federal judges should use for deciding whether expert evidence is to be admitted into a case.1 Before Daubert, there was not a universally followed standard for determining the admissibility of expert evidence in federal courts. The two leading standards were relevance and general acceptance in the expert community. Critics of the relevance standard argued that it let in too much “junk science” because it allowed all evidence that addressed a fact at issue in the case. Critics of the general acceptance standard argued that it excluded novel science that was quite reliable because it deferred to the current consensus in the expert community.
In Daubert, the Supreme Court directed federal judges to examine the method or reasoning underlying the expert evidence and to admit only evidence that was reliable and relevant For scientific evidence, the Supreme Court considered evidence reliable if it was grounded in the methods and procedures of science. No longer can judges defer to the appropriate expert community to determine whether evidence was reliable, and no longer can they leave the determination to the jury. Judges are to act as “gatekeepers,” screening expert evidence to ensure that what is admitted is both relevant and reliable.
In this report, we examine the effects of the new standards for admitting expert evidence into federal court. Our analysis provides strong evidence that the Daubert opinion changed how federal district court judges assess expert evidence in civil cases. It appears that judges are indeed doing what they were directed to do by the Supreme Court: they are increasingly acting as gatekeepers for reliability and relevance, they are examining the methods and reasoning underlying the evidence, and they appear to be employing general acceptance as only one of many factors that enter into their reliability assessments. The rise that took place in both the proportion of evidence found unreliable and the proportion of challenged evidence excluded suggests that the standards for admitting evidence have tightened. The subsequent fall in these two proportions suggests that parties proposing evidence—and perhaps parties challenging evidence as well—have responded to the change in standards.
To explore the effects of Daubert, we statistically analyzed trends in 399 federal district court opinions issued between January 1980 and June 1999 that addressed challenges to expert evidence in civil cases. These challenges, which were brought by plaintiffs, defendants, and____________________