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 performed more efficiently by the Court of Appeals than by the nine members of this Court, I would remand the case to that court for application of the proper standard of review.

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 702,1 as interpreted in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993).2 In general, scientific testimony that is both relevant and reliable must be admitted and testimony that is irrelevant or unreliable must be excluded. Id., at 597. In this case, the District Court relied on both grounds for exclusion.

The relevance ruling was straightforward. The District Court correctly reasoned that an expert opinion that exposure to PCBs, “furans” and “dioxins” together may cause lung cancer would be irrelevant unless the plaintiff had been exposed to those substances. Having already found that there was no evidence of exposure to furans and dioxins, 864 F. Supp. 1310, 1318—1319 (ND Ga. 1994), it necessarily followed that this expert opinion testimony was inadmissible. Correctly applying Daubert, the District Court explained that the experts’ testimony “manifestly does not fit the facts of this case, and is therefore inadmissible.” 864 F. Supp., at 1322. Of course, if the evidence raised a genuine issue of fact on the question of Joiner’s exposure to furans and dioxins–as the Court of Appeals held that it did–then this basis for the ruling on admissibility was erroneous, but not because the district judge either abused her discretion or misapplied the law.3

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.4 They did not suggest that any one study provided adequate support for their conclusions, but instead relied on all the studies taken together (along with their interviews of Joiner and their review of his medical records). The District Court, however, examined the studies one by one and concluded that none was sufficient to show a link between PCBs and lung cancer. 864 F. Supp., at 1324—1326. The focus of the opinion was on the separate studies and the conclusions of the experts, not on the experts’ methodology. Id., at 1322 (“Defendants … persuade the court that Plaintiffs’ expert testimony would not be admissible … by attacking the conclusions that Plaintiffs’ experts draw from the studies they cite”).

Unlike the District Court, the Court of Appeals expressly decided that a “weight of the evidence” methodology was scientifically acceptable.5 To this extent, the Court of Appeals’ opinion is persuasive. It is not intrinsically “unscientific” for experienced professionals to arrive at a conclusion by weighing all available scientific evidence– this is not the sort of “junk science” with which Daubert was concerned.6 After all, as Joiner points out, the Environmental Protection Agency (EPA) uses the same methodology to assess risks, albeit using a somewhat different threshold than that required in a trial. Brief for Respondents 40—41 (quoting EPA, Guidelines for Carcinogen Risk Assessment, 51 Fed. Reg. 33992, 33996 (1986)). Petitioners’ own experts used the same scientific approach as well.7 And using this methodology, it would seem that an expert could reasonably have concluded that the study of workers at an Italian capacitor plant, coupled with data from Monsanto’s study and other studies, raises an inference that PCBs promote lung cancer.8  Next Page ->


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