In Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993), the United States Supreme Court explained that the trial court must act as a "gatekeeper" to ensure both the relevance and the reliability of expert testimony before it is admitted at trial. The court listed factors that a trial court may consider in determining whether expert testimony is relevant and reliable: (1) whether the testimony is based on a theory or method that has or can be tested; (2) whether the testimony is based on a theory or method that has been subject to peer review; (3) the error rate of the particular theory or method; (4) whether the theory or method has gained general acceptance in the field. Id. at 593-594. However, the Court did not intend in listing these factors to design a rigid inquiry; in fact, the Court specifically stated, "Many factors will bear on the inquiry, and we do not presume to set out a definitive checklist or test." The court also noted that the inquiry is to be "flexible." Id. at 594. The Ohio Supreme Court has adopted the Daubert factors. See Miller v. Bike Athletic Co. (1998), 80 Ohio St.3d 607, 1998 Ohio 178, 687 N.E.2d 735. In Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993), 509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469, the United States Supreme Court discussed the question of when expert scientific testimony is relevant and reliable. In Daubert, the court was faced with the issue of whether certain scientific evidence was admissible in a birth defects case. The trial court, in excluding the expert testimony, relied upon Frye v. United States (1923), 54 App.D.C. 46, 293 F. 1013, which held that an expert's opinion is inadmissible unless it has gained "general acceptance" in the relevant scientific community. 293 F. at 1014. The Daubert court expressly rejected this argument and reversed the granting of summary judgment. Instead, it held, under Evid.R. 702, that expert scientific testimony is admissible if it is reliable and relevant to the task at hand. Id. at 589, 113 S.Ct. at 2795, 125 L.Ed.2d at 480. The United States Supreme Court held that in federal cases, the "general acceptance" test of Frye was superseded by the Federal Rules of Evidence (FRE), and thus general acceptance is not a necessary precondition to the admissibility of scientific evidence. The Supreme Court listed several factors for federal judges to consider in determining whether to admit expert scientific testimony under Federal Rules of Evidence rule 702: whether the theory or technique employed by the expert is generally accepted in the scientific community; whether it's been subjected to peer review and publication; whether it can be and has been tested; and whether the known or potential rate of error is acceptable. Id. at 593. The factors are illustrative rather than exhaustive, and each do not need to be applied equally or in every case. Id. Accordingly, Daubert replaced Frye for federal cases, and the standard is liberal. The expert testimony will be admissible if the evidence "will assist the trier of fact to understand or determine a fact in issue." Id. at 591. The United States Supreme Court recognized that the Federal Rules of Evidence require a "trial judge to ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable." Thus, Daubert created a two-part test for determining the admissibility of scientific evidence. Id. at 589, 113 S. Ct. at 2795. However, although a two-part test is to be employed, the threshold issue remains of whether the evidence sought to be admitted is "scientific" evidence or testimony. In Daubert, the Court characterized the word "scientific" as being grounded "in the methods and procedures of science" and "scientific knowledge" as necessitating an inference or assertion which "must be derived by scientific method." Id. at 590. In assessing whether the scientific evidence or testimony is reliable, the Court in Daubert stated that several factors would be relevant, but focused on the following: (1) whether the theory or technique is scientific knowledge that has been tested and, thus, helpful to the trier of fact; (2) whether the technique or theory has been subjected to publication and peer review; (3) the known or potential rate of error; (4) general acceptance within the scientific community. Id. at 593-5. The United States Supreme Court held that Frye's general acceptance requirement had been superseded by the 1975 enactment of Federal Rule of Evidence 702 and rejected Frye as the exclusive test for admitting expert scientific testimony in federal cases. Instead, the Court held that Federal Rule 702 imposes a special obligation upon a trial judge as an evidentiary "gatekeeper" to ensure that scientific evidence is not only relevant but reliable. 509 U.S. at 592-93, 597. The reliability of scientific evidence is to be judged by its scientific validity. Id. at 589 n.9. Under Daubert, the general acceptance test is only one of several factors that a trial court may consider in determining the reliability of a particular scientific theory or technique. 509 U.S. at 592-94. Six years later, in Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 143 L. Ed. 2d 238, 119 S. Ct. 1167 (1999), the Court held that Daubert's gatekeeping obligation is not limited to "scientific" testimony but also applies to "non-scientific" expert testimony. See 526 U.S. at 147-51. The United States Supreme Court interpreted language in Rule 702 of the Federal Rules of Evidence, which at that time was the same as the Arizona rule, and adopted an approach for determining the admissibility of scientific expert testimony that rejected the plain language of the rule and the Frye test as the sole criteria. The Court determined that a trial judge must serve as the "gatekeeper" for determining the admissibility of expert testimony by deciding first, "whether the expert is proposing to testify to: (1) scientific knowledge that; (2) will assist the trier of fact to understand or determine a fact in issue." 509 U.S. at 592, 597. That determination, the Court continued, "entails a preliminary assessment of whether the reasoning or methodology underlying the testimony is scientifically valid and of whether that reasoning or methodology properly can be applied to the facts in issue." Id. at 592-93. The Court suggested four factors for judges to consider in conducting that inquiry: whether the theory or technique "can be (and has been) tested," "whether the theory or technique has been subjected to peer review and publication," "the known or potential rate of error," and whether the theory or technique has been generally accepted by the relevant scientific community. Id. at 593-94.In sum, the Supreme Court asserted that judges, when faced with an offer of expert testimony, must make a preliminary assessment of whether the expert testimony reflects scientific knowledge and an assessment of whether there is a connection between the testimony and the issues in the case.