KUMHO TIRE CO., LTD., et al. v. CARMICHAEL et al.
Engineering testimony rests upon scientific foundations, the reliability of which will be at issue in some cases. See, e.g., Brief for Stephen Bobo et al. as Amici Curiae 23 (stressing the scientific bases of engineering disciplines). In other cases, the relevant reliability concerns may focus upon personal knowledge or experience. As the Solicitor General points out, there are many different kinds of experts, and many different kinds of expertise. See Brief for United States as Amicus Curiae 18—19, and n. 5 (citing cases involving experts in drug terms, handwriting analysis, criminal modus operandi, land valuation, agricultural practices, railroad procedures, attorney’s fee valuation, and others). Our emphasis on the word “may” thus reflects Daubert’s description of the Rule 702 inquiry as “a flexible one.” 509 U.S., at 594. Daubert makes clear that the factors it mentions do not constitute a “definitive checklist or test.” Id., at 593. And Daubert adds that the gatekeeping inquiry must be “ ‘tied to the facts’ ” of a particular “case.” Id., at 591 (quoting United States v. Downing, 753 F.2d 1224, 1242 (CA3 1985)). We agree with the Solicitor General that “[t]he factors identified in Daubert may or may not be pertinent in assessing reliability, depending on the nature of the issue, the expert’s particular expertise, and the subject of his testimony.” Brief for United States as Amicus Curiae 19. The conclusion, in our view, is that we can neither rule out, nor rule in, for all cases and for all time the applicability of the factors mentioned in
Daubert, nor can we now do so for subsets of cases categorized by category of expert or by kind of evidence. Too much depends upon the particular circumstances of the particular case at issue.
Daubert itself is not to the contrary. It made clear that its list of factors was meant to be helpful, not definitive. Indeed, those factors do not all necessarily apply even in every instance in which the reliability of scientific testimony is challenged. It might not be surprising in a particular case, for example, that a claim made by a scientific witness has never been the subject of peer review, for the particular application at issue may never previously have interested any scientist. Nor, on the other hand, does the presence of Daubert’s general acceptance factor help show that an expert’s testimony is reliable where the discipline itself lacks reliability, as, for example, do theories grounded in any so-called generally accepted principles of astrology or necromancy.
At the same time, and contrary to the Court of Appeals’ view, some of Daubert’s questions can help to evaluate the reliability even of experience-based testimony. In certain cases, it will be appropriate for the trial judge to ask, for example, how often an engineering expert’s experience-based methodology has produced erroneous results, or whether such a method is generally accepted in the relevant engineering community. Likewise, it will at times be useful to ask even of a witness whose expertise is based purely on experience, say, a perfume tester able to distinguish among 140 odors at a sniff, whether his preparation is of a kind that others in the field would recognize as acceptable.
We must therefore disagree with the Eleventh Circuit’s holding that a trial judge may ask questions of the sort Daubert mentioned only where an expert “relies on the application of scientific principles,” but not where an expert relies “on skill- or experience-based observation.” 131 F.3d, at 1435. We do not believe that Rule 702 creates a schematism that segregates expertise by type while mapping certain kinds of questions to certain kinds of experts. Life and the legal cases that it generates are too complex to warrant so definitive a match.
To say this is not to deny the importance of Daubert’s gatekeeping requirement. The objective of that requirement is to ensure the reliability and relevancy of expert testimony. It is to make certain that an expert, whether basing testimony upon professional studies or personal experience, employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field. Nor do we deny that, as stated in
Daubert, the particular questions that it mentioned will often be appropriate for use in determining the reliability of challenged expert testimony. Rather, we conclude that the trial judge must have considerable leeway in deciding in a particular case how to go about determining whether particular expert testimony is reliable. That is to say, a trial court should consider the specific factors identified in Daubert where they are reasonable measures of the reliability of expert testimony.
C
The trial court must have the same kind of latitude in deciding how to test an expert’s reliability, and to decide whether or when special briefing or other proceedings are needed to investigate reliability, as it enjoys when it decides whether that expert’s relevant testimony is reliable. Our opinion in Joiner makes clear that a court of appeals is to apply an abuse-of-discretion standard when it “review[s] a trial court’s decision to admit or exclude expert testimony.” 522 U.S., at 138—139. That standard applies as much to the trial court’s decisions about how to determine reliability as to its ultimate conclusion. Otherwise, the trial judge would lack the discretionary authority needed both to avoid unnecessary “reliability” proceedings in ordinary cases where the reliability of an expert’s methods is properly taken for granted, and to require appropriate proceedings in the less usual or more complex cases where cause for questioning the expert’s reliability arises. Indeed, the Rules seek to avoid “unjustifiable expense and delay” as part of their search for “truth” and the “jus[t]
determin[ation]” of proceedings. Fed. Rule Evid. 102. Thus, whether Daubert’s specific factors are, or are not, reasonable measures of reliability in a particular case is a matter that the law grants the trial judge broad latitude to determine. See Joiner, supra, at 143. And the Eleventh Circuit erred insofar as it held to the contrary.
III
We further explain the way in which a trial judge “may” consider Daubert’s factors by applying these considerations to the case at hand, a matter that has been briefed exhaustively by the parties and their 19
amici. The District Court did not doubt Carlson’s qualifications, which included a masters degree in mechanical engineering, 10 years’ work at Michelin America, Inc., and testimony as a tire failure consultant in other tort cases. Rather, it excluded the testimony because, despite those qualifications, it initially doubted, and then found unreliable, “the methodology employed by the expert in analyzing the data obtained in the visual inspection, and the scientific basis, if any, for such an analysis.”
Civ. Action No. 93—0860—CB—S (SD Ala., June 5, 1996), App. to Pet. for Cert. 6c. After examining the transcript in “some detail,” 923 F. Supp., at 1518—519, n. 4, and after considering respondents’ defense of Carlson’s methodology, the District Court determined that Carlson’s testimony was not reliable. It fell outside the range where experts might reasonably differ, and where the jury must decide among the conflicting views of different experts, even though the evidence is “shaky.”
Daubert, 509 U.S., at 596. In our view, the doubts that triggered the District Court’s initial inquiry here were reasonable, as was the court’s ultimate
conclusion.
For one thing, and contrary to respondents’ suggestion, the specific issue before the court was not the reasonableness in general of a tire expert’s use of a visual and tactile inspection to determine whether overdeflection had caused the tire’s tread to separate from its steel-belted carcass. Rather, it was the reasonableness of using such an approach, along with Carlson’s particular method of analyzing the data thereby obtained, to draw a conclusion regarding the particular matter to which the expert testimony was directly relevant. That matter concerned the likelihood that a defect in the tire at issue caused its tread to separate from its carcass. The tire in question, the expert conceded, had traveled far enough so that some of the tread had been worn bald; it should have been taken out of service; it had been repaired (inadequately) for punctures; and it bore some of the very marks that the expert said indicated, not a defect, but abuse through
overdeflection. See supra, at 3—5; App. 293—294. The relevant issue was whether the expert could reliably determine the cause of this tire’s separation.
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