AuthorSchroeder, Thomas D.


Over a quarter century ago, Daubert v. Merrell Dow Pharmaceuticals, Inc. reaffirmed the trial court's role as "gatekeeper" for the admission of scientific expert evidence, to screen it not only for relevance, but for reliability. (1) To dischargethis gatekeeper role, a trial court must make a preliminary determination whetherthe expert's opinion evidence meets the admissibility standards of Federal Rule of Evidence 702, which in turn requires application of FederalRule of Evidence 104(a)'s preponderance test. Trial judges are cautioned not to unduly assess the validity or strength of an expert's scientific conclusions, and the Supreme Court has said that "shaky but admissible evidence" (2) should be left for a jury's consideration where it can be tested by cross-examination and contrary evidence. But application of these principles canbe difficult, and appellate review can be frustrated, even under a deferential abuse of discretion standard, where trial courts are not clear about what standard they are applying. Worse, some trial and appellate courts misstate andmuddle the admissibility standard, suggesting that questions of the sufficiency of the expert's basis and the reliability of the application of the expert's method raise questions of weight that should be resolved by a jury, where they can be subject to cross-examination and competing evidence. The state of affairs has prompted the United States Judicial Conference's Advisory Committee on the Federal Rules of Evidence to consider possible amendment to Rule 702 to reiterate the need for proper application of Rule 104(a)'s threshold to each requirement of Rule 702.

This Article highlights lingering confusion in the caselaw as to the proper standard for the trial court's discharge of its gatekeeping role for the admission of expert testimony. The Article urges correction of the faulty application of Daubert's admonition as to "shaky but admissible" evidence as a substitute for proper discharge of the trial court's gatekeeper function under Rule 104(a). The Article concludes with several suggestions for trial and appellate courts to consider for better decisionmaking in discharging their duty to apply Rule 104(a)'s preponderance standard to the elements of Rule 702.


    In 1993, the Supreme Court decided Daubert, a personal injury case involvingan antinausea drug, and revolutionized how trial courts are to consider the admission of scientific and technical expert evidence. In eschewing the Frye (3) "general acceptance" test as inconsistent with the "liberal thrust" of the subsequent Federal Rules of Evidence, (4) the Court simultaneously expanded and restricted the availability of expert testimony. It liberalized the availability of evidence because the Frye test became, under the language ofRule 702, but one of several factors for a court to consider when determining whether the proffered evidence is valid and reliable: whether the theory or technique can be (or has been) tested; whether it has been subjected to peerreview and publication; its known or potential rate of error; the existence and maintenance of standards controlling its operation; and whether it has attracted "widespread acceptance within a relevant scientific community." (5) At the same time, the Court tightened the admissibility threshold by chargingtrial judges to act as "gatekeepers" against the admission of unreliable expert opinion. (6) In doing so, the Court reminded trial judges that, as withother questions of preliminary admissibility, a court "[f]aced with a proffer of expert scientific testimony... must determine at the outset... whether the expert is proposing to testify to (1) scientific knowledge that (2) will assist the trier of fact to understand or determine a fact in issue." (7) In a footnote, the Court noted that "[t]hese matters should be established by a preponderance of proof," pursuant to Rule 104(a). (8)

    Rule 702 was amended in 2000. (9) In addition to requiring that the expert be qualified to testify about scientific knowledge that will assist the trier of fact, the Rule added further foundational requirements, now found in sections (b), (c), and (d), that the testimony be based on sufficient facts or data, the testimony be the product of reliable principles and methods, and the expert have reliably applied the principles and methods to the facts of the case, respectively. (10) In light of Daubert's reference to Rule 104(a), the AdvisoryCommittee expressly stated that the trial judge determine these elements by a preponderance before allowing such testimony into evidence. (11) The extensive Advisory Committee note further explained the limits of the preponderancestandard in this context. For example, competing and contradictory expert testimony can meet the standard, as proponents "do not have to demonstrate to the judge by a preponderance of the evidence that the assessments of their experts are correct," but only that "their opinions are reliable"--a lesser standard. (12) Moreover, the standard can be met even where competing experts rely on competing versions of the facts, as it is not the trial judge's role to believe one version of the facts over another.

    After Daubert, the Court has clarified that this gatekeeper function applies to all expert testimony, not just that based on science. (13) Over the years, courts have supplemented the various Daubert factors for determining reliability. They include whether the opinions are litigation driven, or naturally flow from independent scientific research; whether the expert has accounted for obvious alternative explanations; whether the expert has employed the same level of rigor as required in the relevant field; and whether the field of expertise is known to reach reliable results. (14)

    Ever since Daubert, the Court has expressed conflicting views on the ease with which trial judges will be able to discharge their gatekeeper role. (15) For example,in General Electric Co. v. Joiner, (16) the Court retrenched from its previous admonition against judging the strength of an expert's conclusions by recognizing that on occasion an expert may "unjustifiably extrapolate[ ] from an accepted premise to an unfounded conclusion" (17) such that the trial judge may find that there is "simply too great an analytical gap between the data and the opinion proffered" to rely on the expert's ipse dixit to make the connection. (18) Justice Breyer, after acknowledging that Daubert "ask[s] judges tomake subtle and sophisticated determinations" about scientific methodology andits relation to the conclusions offered by an expert witness, nevertheless predicted that given the "offer of cooperative effort" from the scientific community (there, the New England Journal of Medicine) and the "various Rules-authorized methods for facilitating the [trial] courts' task" (such as appointing a Rule 706 (19) advisory expert), implementing Daubert's gatekeeping task "will not prove inordinately difficult." (20) Justice Stevens, in contrast, noted that "Daubert quite clearly forbids trial judges to assess the validity or strength of an expert's scientific conclusions, which is a matter for the jury." (21) Justice Stevens saw a distinct difference between methodology and conclusions,relying on Daubert's statement that "[v]igorous cross-examination, presentationof contrary evidence, and careful instruction on the burden of proof are the traditional and appropriate means of attacking shaky but admissible evidence." (22)

    Not only is it "not always a straightforward exercise to disaggregate method and conclusion," (23) it is also not always easy to assess when the Rule's foundational requirements--namely, sufficiency of the basis of a proposed opinion and whether the opinion resulted from reliable application of valid principles and methods--falls short of the preponderance standard for threshold admissibility. While courts no doubt acknowledge and grapple with the issue before determining admissibility, some courts have defaulted toinvoking the Supreme Court's caution that Rule 702 is not meant to prohibit "shaky but admissible" evidence and have relegated the issue to the jury's consideration on the grounds it can be subject to cross-examination and contrary proof. In doing so, some of these courts have inadvertently applied Rule 104(b)'s standard for admissibility, in contravention of Daubert. (24) Some courts merely find that there is sufficient evidence, if believed, for a reasonable juror to find that the expert has a sufficient basis for his opinion or that he reliably applied the principles and methods he claims. Other courts conclude that the application of a valid methodology should be deemed unreliable only if it skews the methodology itself. Rule 104(a) and theDaubert line of cases require, however, that the trial judge actually determine whetherit is more likely than not that the expert has met these threshold requirements of Rule 702.

    In this respect, therefore, some courts appear to be abdicating their charge under the Federal Rules of Evidence and Daubert and its progeny to makethe hard call on admissibility. The end result in such cases is to relegate to the jury the very decisions Rule 702 contemplates to be beyond jury consideration. In other cases, however, it is more difficult to tell what the courts are actually doing, as they do not articulate their reasoning in a way that demonstrates how they are applying the preponderance standard to the required elements of the Rule.


    Numerous cases have stated that questions as to sufficiency of basis or reliability of application raise questions of weight that are necessarily for a jury, and not questions of admissibility for the court. Some of these courts may very well have actually applied Rule 104(a)'s standard; or, they may have applied Rule 104(b)'s...

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