Daubert, the majority opinion in Daubert stated that the trial court has not only the power but the obligation to act as gatekeeper.8

The Court then considered the meaning of its two-pronged test of relevancy and reliability in the context of scientific evidence. With regard to relevancy, the Court explained that expert testimony cannot assist the trier in resolving a factual dispute, as required by Rule 702, unless the expert’s theory is tied sufficiently to the facts of the case. “Rule 702’s ‘helpfulness’ standard requires a valid scientific connection to the pertinent inquiry as a precondition to admissibility.”9 This consideration, the Court remarked, “has been aptly described by Judge Becker as one of ‘fit.’”10

To determine whether proffered scientific testimony or evidence satisfies the standard of evidentiary reliability,11 a judge must ascertain whether it is “ground[ed] in the methods and procedures of science.”12 The Court, emphasizing that “[t]he inquiry envisioned by Rule 702 is…a flexible one,”13 then examined the characteristics of scientific methodology and set out a nonexclusive list of four factors that bear on whether a theory or technique has been derived by the scientific method.14 First and foremost, the Court viewed science as an empirical endeavor: “[W]hether [a theory or technique] can be (and has been) tested” is the “methodology [that] distinguishes science from other fields of human inquiry.”15 The Court also mentioned as indicators of good science whether the technique or theory has been subjected to peer review or publication, whether the existence of known or potential error rates has been determined, and whether standards exist for controlling the technique’s operation.16 In addition, although general acceptance of the methodology within the scientific community is no longer dispositive, it remains a factor to be considered.17

The Court did not apply its new test to the eight experts for the plaintiffs who sought to testify on the basis of in vitro, animal, and epidemiological studies

8. Id.

9. Id. at 591–92.

10. Id. at 591. Judge Becker used this term in discussing the admissibility of expert testimony about factors that make eyewitness testimony unreliable. See United States v. Downing, 753 F.2d 1224, 1242 (3d Cir. 1985) (on remand court rejected the expert testimony on ground of “fit” because expert discussed factors such as the high likelihood of inaccurate cross-racial identifications that were not present in the case) and United States v. Downing, 609 F. Supp. 784, 791–92 (E.D. Pa. 1985), aff’d, 780 F.2d 1017 (3d Cir. 1985).

11. Commentators have faulted the Court for using the label “reliability” to refer to the concept that scientists term “validity.” The Court’s choice of language was deliberate. It acknowledged that scientists typically distinguish between validity and reliability and that “[i]n a case involving scientific evidence, evidentiary reliability will be based upon scientific validity.” Daubert, 509 U.S. at 590 n.9.

12. Id. at 590.

13. Id. at 594.

14. Id. at 593–94. “[W]e do not presume to set out a definitive checklist or test.” Id. at 593.

15. Id.

16. Id. at 593–94.

17. Id. at 594.

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