“and a rigid ‘general acceptance’ requirement would be at odds with the ‘liberal thrust’ of the Federal Rules and their ‘general approach of relaxing the traditional barriers to ‘opinion’ testimony.’”23 The Court indicated that the subject of expert testimony should be “scientific knowledge,” so “evidentiary reliability will be based upon scientific validity.”24 The Court also emphasized that, in considering the admissibility of evidence, trial judges should focus “solely” on experts’ “principles and methodology,” and “not on the conclusions that they generate.”25 In sum, Daubert’s requirement that expert testimony pertain to “scientific knowledge” established a standard of “evidentiary reliability.”

In explaining this evidentiary standard, the Daubert Court pointed to several factors that might be considered by a trial judge: (1) whether a theory or technique can be (and has been) tested; (2) whether the theory or technique has been subjected to peer review and publication; (3) the known or potential rate of error of a particular scientific technique; (4) the existence and maintenance of standards controlling the technique’s operation; and (5) a scientific technique’s degree of acceptance within a relevant scientific community.26 In the end, however, the Court emphasized that the inquiry under Rule 702 is “a flexible one.”27 The Court also rejected the suggestion that its liberal construction of Rule 702 would “result in a ‘free-for-all’ in which befuddled juries are confounded by absurd and irrational pseudoscientific assertions.”28 Rather, the Court expressed confidence in the adversary system, noting that “[v]igorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof are the traditional and appropriate means of attacking shaky but admissible evidence.”29


Ibid., p. 588 (internal citations omitted).


Ibid, p. 590 and n.9 (emphasis omitted).


Ibid., p. 595. In General Electric Co. v. Joiner, 522 U.S. 136, 146 (1997), the Court added: “[C]onclusions and methodology are not entirely distinct from one another. Trained experts commonly extrapolate from existing data. But nothing in 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.”


Ibid., pp. 592-94.


Ibid., p. 594. In Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137 (1999), the Court confirmed that the Daubert factors do not constitute a definitive checklist or test. Kumho Tire importantly held that Rule 702 applies to both scientific and nonscientific expert testimony; the Court also indicated that the Daubert factors might be applicable in a trial judge’s assessment of the reliability of nonscientific expert testimony, depending upon “the particular circumstances of the particular case at issue.” 526 U.S. at 150.


Daubert, 509 U.S. at 595.


Ibid., p. 596.

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