"As in political revolutions, so in paradigm
choice -- there is
--Thomas Kuhn, The Structure of Scientific Revolutions
In Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999), the Supreme Court disposed once and for all of the notion that Daubert's gatekeeping principles might extend only to scientific testimony. Invoking the requirement of Fed. R. Evid. 702 that expert testimony embody scientific, technical, or other specialized knowledge, the Court held that trial courts ruling on admissibility must evaluate the "reliability" of all expert testimony, whether scientific or not. Emphasizing Daubert's "flexible" approach, the Court noted that the factors bearing on a reliability determination may vary depending on the field of expertise. Mechanics, for example, presumably do not frequently author published, peer-reviewed studies in learned journals. But in every field, the need to evaluate the trustworthiness of the expert's methodology remains.
The Daubert decision was itself breathtakingly ambitious insofar as it set judges the project of evaluating what should and should not count as "science" -- a question on which scientists themselves have never reached agreement and probably never will. But that already daunting project pales by comparison with the judicial task, imposed by Kumho Tire, of evaluating what will and will not count as "scientific, technical, or other specialized" knowledge. Unsurprisingly, the Kumho Tire opinion does not offer any handy formula, applicable in all domains of human inquiry, for conducting this evaluation. The district courts, it says, must have "considerable leeway."
When in Rome . . . .
Still, the Kumho Tire opinion does offer one benchmark. The expert should conduct his or her courtroom analyses, the Court says, under the same standards for "intellectual rigor" that generally prevail in the expert's field.
In supplying this benchmark, the Court can be seen as taking a relativist turn. In its Daubert opinion, the Court seemed to be searching for an objective definition of "the scientific method" -- a set of fixed intellectual criteria against which to measure all claims that knowledge should count as scientific. This was, of course, a quixotic enterprise, as many generations of philosophers and scientists have discovered in the course of making similar attempts. In the end, therefore, it is understandable if the Court in Daubert was unable to develop any truly criterial definition of "science." The best it could do was to list some important "factors" that seemed to bear on the problem. Even that modest result, however, had a decidedly objectivist flavor. In the Daubert Court's world, science (or physical science, at least) is a process whereby investigators employ a canonical set of methods to develop theories, like the law of gravitation, that are tested against empirical data in experiments, with the results being measured quantitatively, so that the theories may be revised or refined, ever more closely approximating the truth -- i.e., an accurate depiction of the natural laws that actually govern the natural world.
This view of science can fairly be criticized as naive and outdated. Still, it does comport with the heroic ambition of many practicing scientists to adhere to some independent canons of rational inquiry, under which investigators try to survey the world as it actually presents itself, and not as some prevailing orthodoxy would like the world to be. And as Thomas Kuhn, among others, has reminded us, the reigning scientific orthodoxies may sometimes represent just as serious an impediment to scientific "progress" as any religious or political ideology has ever done. For this reason, science itself does not test knowledge by polling the scientific tribe to see what the tribe already believes. A legal standard that would make those tribal beliefs the touchstone -- e.g., the Frye test -- can likewise be seen as anathema to the scientific ideal, and it is natural to appeal to familiar emblems of independent rationality, like the Scientific Method, in the effort to find something better.
In Kumho Tire, however, the Court seems to retreat from Daubert's objectivist stance. The standard for "intellectual rigor" is defined, in Kumho Tire, not by appeal to the True Rules of Rational Inquiry, to which some brooding omnipresence in the sky might adhere, but rather by reference to the norms prevailing among practitioners of the expert's own field. This is not the same, to be sure, as a rule making expert testimony admissible if and only if the testimony is founded on methods generally accepted in the expert's discipline. But it does seem close to an admission, by the Court, that in evaluating whether testimony from a given field of expertise is competent, one could do a lot worse than consult the standards for inquiry prevalent in that field.
Some Dicta on Procedure
Part II(C) of the Kumho Tire opinion also includes a seemingly gratuitous treatment of the procedures by which courts should conduct their Daubert/Kumho analyses. The gist of the Court's discussion on this subject is that the district courts should enjoy discretion not only as to the substance of their Daubert/Kumho analyses but also as to the procedures through which such evidentiary issues are resolved. Proceedings need not be extensive in "ordinary cases" where the reliability of an expert is "properly taken for granted," but "appropriate proceedings" should be held in "less usual or more complex" cases when the necessity appears. The Eleventh Circuit erred, the opinion says, "insofar as it held to the contrary" -- though it is actually hard to see anyplace in the Eleventh Circuit's opinion where the lower court could be thought to have ruled on this issue at all.