Chief Justice Rehnquist delivered the opinion of the Court.
We granted certiorari in this case to determine what standard an appellate court should apply in reviewing a trial
Respondent Robert Joiner began work as an electrician in the Water & Light Department of Thomasville, Georgia (City), in 1973. This job required him to work with and around the City's electrical transformers, which used a mineral-oil-based dielectric fluid as a coolant. Joiner often had to stick his hands and arms into the fluid to make repairs. The fluid would sometimes splash onto him, occasionally getting into his eyes and mouth. In 1983 the City discovered that the fluid in some of the transformers was contaminated with polychlorinated biphenyls (PCB's). PCB's are widely considered to be hazardous to human health. Congress, with limited exceptions, banned the production and sale of PCB's in 1978. See 90 Stat. 2020, 15 U. S. C. § 2605(e)(2)(A).
Joiner was diagnosed with small-cell lung cancer in 1991. He
Petitioners removed the case to federal court. Once there, they moved for summary judgment. They contended that (1) there was no evidence that Joiner suffered significant exposure to PCB's, furans, or dioxins, and (2) there was no admissible scientific evidence that PCB's promoted Joiner's cancer. Joiner responded that there were numerous disputed factual issues that required resolution by a jury. He relied largely on the testimony of expert witnesses. In depositions, his experts had testified that PCB's alone can promote cancer and that furans and dioxins can also promote cancer. They opined that since Joiner had been exposed to PCB's, furans, and dioxins, such exposure was likely responsible for Joiner's cancer.
The District Court ruled that there was a genuine issue of material fact as to whether Joiner had been exposed to PCB's. But it nevertheless granted summary judgment for petitioners because (1) there was no genuine issue as to whether Joiner had been exposed to furans and dioxins, and (2) the testimony of Joiner's experts had failed to show that there was a link between exposure to PCB's and small-cell lung cancer. The court believed that the testimony of respondent's experts to the contrary did not rise above "subjective belief or unsupported speculation." 864 F.Supp. 1310, 1326 (ND Ga. 1994). Their testimony was therefore inadmissible.
The Court of Appeals for the Eleventh Circuit reversed. 78 F.3d 524 (1996). It held that "[b]ecause the Federal Rules of Evidence governing expert testimony display a preference for admissibility, we apply a particularly stringent standard of review to the trial judge's exclusion of expert testimony." Id., at 529. Applying that standard, the Court of Appeals held that the District Court had erred in excluding the testimony of Joiner's expert witnesses. The
We granted petitioners' petition for a writ of certiorari, 520 U.S. 1114 (1997), and we now reverse.
Petitioners challenge the standard applied by the Court of Appeals in reviewing the District Court's decision to exclude respondent's experts' proffered testimony. They argue that that court should have applied traditional "abuse of discretion" review. Respondent agrees that abuse of discretion is the correct standard of review. He contends, however, that the Court of Appeals applied an abuse-of-discretion standard in this case. As he reads it, the phrase "particularly stringent" announced no new standard of review. It was simply an acknowledgment that an appellate court can and will devote more resources to analyzing district court decisions that are dispositive of the entire litigation. All evidentiary decisions are reviewed under an abuse-of-discretion standard. He argues, however, that it is perfectly reasonable for appellate courts to give particular attention to those decisions that are outcome determinative.
We have held that abuse of discretion is the proper standard of review of a district court's evidentiary rulings. Old Chief v. United States, 519 U.S. 172, 174, n. 1 (1997); United States v. Abel, 469 U.S. 45, 54 (1984). Indeed, our cases on
Thus, while the Federal Rules of Evidence allow district courts to admit a somewhat broader range of scientific testimony than would have been admissible under Frye, they leave in place the "gatekeeper" role of the trial judge in screening such evidence. A court of appeals applying "abuse-of-discretion" review to such rulings may not categorically distinguish between rulings allowing expert testimony and rulings disallowing it. Compare Beech Aircraft Corp. v. Rainey, 488 U.S. 153, 172 (1988) (applying abuse-ofdiscretion review to a lower court's decision to exclude evidence), with United States v. Abel, supra, at 54 (applying abuse-of-discretion review to a lower court's decision to admit evidence). We likewise reject respondent's argument that because the granting of summary judgment in this case
We hold that the Court of Appeals erred in its review of the exclusion of Joiner's experts' testimony. In applying an overly "stringent" review to that ruling, it failed to give the trial court the deference that is the hallmark of abuse-ofdiscretion review. See, e. g., Koon v. United States, 518 U.S. 81, 98-99 (1996).
We believe that a proper application of the correct standard of review here indicates that the District Court did not abuse its discretion. Joiner's theory of liability was that his exposure to PCB's and their derivatives "promoted" his development of small-cell lung cancer. In support of that theory he proffered the deposition testimony of expert witnesses. Dr. Arnold Schecter testified that he believed it "more likely than not that Mr. Joiner's lung cancer was causally linked to cigarette smoking and PCB exposure." App. 107. Dr. Daniel Teitelbaum testified that Joiner's "lung cancer was caused by or contributed to in a significant degree by the materials with which he worked." Id., at 140.
Petitioners contended that the statements of Joiner's experts regarding causation were nothing more than speculation. Petitioners criticized the testimony of the experts in that it was "not supported by epidemiological studies . . . [and was] based exclusively on isolated studies of laboratory animals." 3 Record, Doc. No. 46 (Defendants' Joint Memorandum in Support of Summary Judgment 3). Joiner responded by claiming that his experts had identified "relevant animal studies which support their opinions." 4 Record, Doc. No. 53 (Plaintiffs' Brief in Opposition to Defendants'
The District Court agreed with petitioners that the animal studies on which respondent's experts relied did not support his contention that exposure to PCB's had contributed to his cancer. The studies involved infant mice that had developed cancer after being exposed to PCB's. The infant mice in the studies had had massive doses of PCB's injected directly into their peritoneums
Respondent failed to reply to this criticism. Rather than explaining how and why the experts could have extrapolated their opinions from these seemingly far-removed animal studies, respondent chose "to proceed as if the only issue [was] whether animal studies can ever be a proper foundation for an expert's opinion." 864 F. Supp., at 1324. Of course, whether animal studies can ever be a proper foundation for an expert's opinion was not the issue. The issue was whether these experts' opinions were sufficiently supported by the animal studies on which they purported to rely. The studies were so dissimilar to the facts presented in this litigation
The District Court also concluded that the four epidemiological studies on which respondent relied were not a sufficient basis for the experts' opinions. The first such study involved workers at an Italian capacitor
The second study followed employees who had worked at Monsanto's PCB production plant. J. Zack & D. Musch, Mortality of PCB Workers at the Monsanto Plant in Sauget, Illinois (Dec. 14, 1979) (unpublished report), 3 Record, Doc. No. 11. The authors of this study found that the incidence of lung cancer deaths among these workers was somewhat higher than would ordinarily be expected. The increase, however, was not statistically significant and the authors of the study did not suggest a link between the increase in lung cancer deaths and the exposure to PCB's.
The third and fourth studies were likewise of no help. The third involved workers at a Norwegian cable manufacturing company who had been exposed to mineral oil. Ronneberg, Andersen, & Skyberg, Mortality and Incidence of Cancer Among Oil Exposed Workers in a Norwegian Cable Manufacturing Company, 45 British Journal of Industrial
Respondent points to Daubert `s language that the "focus, of course, must be solely on principles and methodology, not on the conclusions that they generate." 509 U. S., at 595. He claims that because the District Court's disagreement was with the conclusion that the experts drew from the studies, the District Court committed legal error and was properly reversed by the Court of Appeals. But conclusions and methodology are not entirely distinct from one another. Trained experts commonly extrapolate from existing data. But nothing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence that is connected to existing data only by the ipse dixit of the expert. A court may conclude that there is simply too great an analytical gap between the data and the opinion proffered. See Turpin v. Merrell Dow Pharmaceuticals, Inc. , 959 F.2d 1349, 1360 (CA6), cert. denied, 506 U.S. 826 (1992). That is what the District Court did here, and we hold that it did not abuse its discretion in so doing.
We hold, therefore, that abuse of discretion is the proper standard by which to review a district court's decision to admit or exclude scientific evidence. We further hold that, because it was within the District Court's discretion to conclude that the studies upon which the experts relied were not
Respondent's original contention was that his exposure to PCB's, furans, and dioxins contributed to his cancer. The District Court ruled that there was a genuine issue of material fact as to whether Joiner had been exposed to PCB's, but concluded that there was no genuine issue as to whether he had been exposed to furans and dioxins. The District Court accordingly never explicitly considered if there was admissible evidence on the question whether Joiner's alleged exposure to furans and dioxins contributed to his cancer. The Court of Appeals reversed the District Court's conclusion that there had been no exposure to furans and dioxins. Petitioners did not challenge this determination in their petition to this Court. Whether Joiner was exposed to furans and dioxins, and whether if there was such exposure, the opinions of Joiner's experts would then be admissible, remain open questions. We accordingly reverse the judgment of the Court of Appeals and remand this case for proceedings consistent with this opinion.
It is so ordered.
Justice Breyer, concurring.
The Court's opinion, which I join, emphasizes Daubert `s statement that a trial judge, acting as "gatekeeper," must "`ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable.' " Ante, at 142 (quoting Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 589 (1993)). This requirement will sometimes ask judges to make subtle and sophisticated determinations about scientific methodology and its relation to the conclusions an expert witness seeks to offer—particularly when a case arises in an area where the science itself is tentative or
Of course, neither the difficulty of the task nor any comparative lack of expertise can excuse the judge from exercising the "gatekeeper" duties that the Federal Rules of Evidence impose—determining, for example, whether particular expert testimony is reliable and "will assist the trier of fact," Fed. Rule Evid. 702, or whether the "probative value" of testimony is substantially outweighed by risks of prejudice, confusion or waste of time, Fed. Rule Evid. 403. To the contrary, when law and science intersect, those duties often must be exercised with special care.
Today's toxic tort case provides an example. The plaintiff in today's case says that a chemical substance caused, or promoted, his lung cancer. His concern, and that of others, about the causes of cancer is understandable, for cancer kills over one in five Americans. See U. S. Dept. of Health and Human Services, National Center for Health Statistics, Health, United States 1996-97 and Injury Chartbook 117 (1997) (23.3% of all deaths in 1995). Moreover, scientific evidence implicates some chemicals as potential causes of some cancers. See, e. g., U. S. Dept. of Health and Human Services, Public Health Service, National Toxicology Program, 1 Seventh Annual Report on Carcinogens, pp. v—vi (1994). Yet modern life, including good health as well as economic well-being, depends upon the use of artificial or manufactured substances, such as chemicals. And it may, therefore, prove particularly important to see that judges fulfill their Daubert gatekeeping function, so that they help assure that the powerful engine of tort liability, which can generate
I therefore want specially to note that, as cases presenting significant science-related issues have increased in number, see Judicial Conference of the United States, Report of the Federal Courts Study Committee 97 (Apr. 2, 1990) ("Economic, statistical, technological, and natural and social scientific data are becoming increasingly important in both routine and complex litigation"), judges have increasingly found in the Rules of Evidence and Civil Procedure ways to help them overcome the inherent difficulty of making determinations about complicated scientific, or otherwise technical, evidence. Among these techniques are an increased use of Rule 16's pretrial conference authority to narrow the scientific issues in dispute, pretrial hearings where potential experts are subject to examination by the court, and the appointment of special masters and specially trained law clerks. See J. Cecil & T. Willging, Court-Appointed Experts: Defining the Role of Experts Appointed Under Federal Rule of Evidence 706, pp. 83-88 (1993); J. Weinstein, Individual Justice in Mass Tort Litigation 107-110 (1995); cf. Kaysen, In Memoriam: Charles E. Wyzanski, Jr., 100 Harv. L. Rev. 713, 713-715 (1987) (discussing a judge's use of an economist as a law clerk in United States v. United Shoe Machinery Corp., 110 F.Supp. 295 (Mass. 1953), aff'd, 347 U.S. 521 (1954)).
In the present case, the New England Journal of Medicine has filed an amici brief "in support of neither petitioners nor respondents" in which the Journal writes:
Cf. Fed. Rule Evid. 706 (court may "on its own motion or on the motion of any party" appoint an expert to serve on behalf of the court, and this expert may be selected as "agreed upon by the parties" or chosen by the court); see also Weinstein, supra, at 116 (a court should sometimes "go beyond the experts proffered by the parties" and "utilize its powers to appoint independent experts under Rule 706 of the Federal Rules of Evidence"). Given this kind of offer of cooperative effort, from the scientific to the legal community, and given the various Rules-authorized methods for facilitating the courts' task, it seems to me that Daubert `s gatekeeping requirement will not prove inordinately difficult to implement, and that it will help secure the basic objectives of the Federal Rules of Evidence, which are, to repeat, the ascertainment of truth and the just determination of proceedings. Fed. Rule Evid. 102.
Justice Stevens, concurring in part and dissenting in part.
The question that we granted certiorari to decide is whether the Court of Appeals applied the correct standard of review. That question is fully answered in Parts I and II of the Court's opinion. Part III answers the quite different question whether the District Court properly held that the testimony of plaintiff's expert witnesses was inadmissible. Because I am not sure that the parties have adequately briefed that question, or that the Court has adequately explained why the Court of Appeals' disposition was erroneous, I do not join Part III. Moreover, because a proper answer to that question requires a study of the record that can be
One aspect of the record will illustrate my concern. As the Court of Appeals pointed out, Joiner's experts relied on "the studies of at least thirteen different researchers, and referred to several reports of the World Health Organization that address the question of whether PCBs cause cancer." 78 F.3d 524, 533 (CA11 1996). Only one of those studies is in the record, and only six of them were discussed in the District Court opinion. Whether a fair appraisal of either the methodology or the conclusions of Joiner's experts can be made on the basis of such an incomplete record is a question that I do not feel prepared to answer.
It does seem clear, however, that the Court has not adequately explained why its holding is consistent with Federal Rule of Evidence 702,
The relevance ruling was straightforward. The District Court correctly reasoned that an expert opinion that exposure
The reliability ruling was more complex and arguably is not faithful to the statement in Daubert that "[t]he focus, of course, must be solely on principles and methodology, not on the conclusions that they generate." 509 U. S., at 595. Joiner's experts used a "weight of the evidence" methodology to assess whether Joiner's exposure to transformer fluids promoted his lung cancer.
Unlike the District Court, the Court of Appeals expressly decided that a "weight of the evidence" methodology was scientifically acceptable.
The Court of Appeals' discussion of admissibility is faithful to the dictum in Daubert that the reliability inquiry must focus on methodology, not conclusions. Thus, even though I fully agree with both the District Court's and this Court's explanation of why each of the studies on which the experts relied was by itself unpersuasive, a critical question remains unanswered: When qualified experts have reached relevant conclusions on the basis of an acceptable methodology, why are their opinions inadmissible?
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.
In any event, it bears emphasis that the Court has not held that it would have been an abuse of discretion to admit the expert testimony. The very point of today's holding is that the abuse-of-discretion standard of review applies whether the district judge has excluded or admitted evidence. Ante, at 142. And nothing in either Daubert or the Federal Rules of Evidence requires a district judge to reject an expert's conclusions and keep them from the jury when they fit the facts of the case and are based on reliable scientific methodology.
Accordingly, while I join Parts I and II of the Court's opinion, I do not concur in the judgment or in Part III of its opinion.
Briefs of amici curiae urging affirmance were filed for the Trial Lawyers for Public Justice by Steven E. Fineman and Arthur H. Bryant; for the Association of Trial Lawyers of America by Jeffrey Robert White; for Ardith Cavallo by William A. Beeton, Jr.; and for Peter Orris, M. D., et al. by Gerson H. Smoger.
Briefs of amici curiae were filed for the New England Journal of Medicine et al. by Margaret S. Woodruff and Arlin M. Adams; and for the Product Liability Advisory Council, Inc., et al. by Mary A. Wells, Jan S. Amundson, and Quentin Riegel.