In 1923, the U.S. District Court for the District of Columbia announced the Frye test, which required a proponent of scientific evidence to establish that the expert witness’s theory and method were generally accepted within the relevant scientific community. Frye v. United States, 293 F. 1013 (D.C. Cir. 1923). In Frye, the court explained: Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs. Frye, 293 F. at 1014. Essentially, the Frye test involves a two-step analysis: (1) defining the relevant scientific community, and (2) evaluating the testimony and publications to determine the existence of a general consensus. At its core, the purpose of the Frye test is to ensure that ‘‘the scientific theory or discovery from 3 which an expert derives an opinion is reliable. Although criticized, the Frye test was adopted by many states and federal courts, remaining the dominant test until 1993, when the U.S. Supreme Court announced a new standard for determining the admissibility of scientific evidence in Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). In Daubert, the Court reviewed the Frye test ‘‘in light of sharp divisions among the courts regarding the proper standard for the admission of expert testimony’’ and held that Federal Rule of Evidence 702 (‘‘FRE 702’’) superseded the Frye test. Id. at 585–87. Establishing a ‘‘gate keeping’’ role for the trial judge, the Daubert Court identified several factors to be considered in determining the admissibility of scientific evidence. Id. at 592-94. The Court retained ‘‘general acceptance’’ within the relevant scientific community as one factor, but it was no longer the exclusive test for determining admissibility; additional factors to be considered include whether the method can and has been tested, whether it has been subjected to peer review and publication, and the known or potential error rate. Id. at 593-94. Emphasizing the new standard’s flexibility, the Court explained that ‘‘[i]ts overarching subject is the scientific validity and thus the evidentiary relevance and reliability of the principles that underlie a proposed submission. The focus, of course, must be solely on principles and methodology, not on the conclusions that they generate.’’ Id. at 594–95. Because the Daubert decision was based on the language of FRE 702, rather than constitutional grounds, states were not required to adopt its standard for the admissibility of expert testimony. Since Daubert, some states have continued to apply Frye, others have explicitly rejected Frye and adopted the more liberal Daubert standards or a similar test, and others still have adhered to their own unique tests.
When the Supreme Court issued its opinion in Daubert, it suggested four criteria for determining whether science was reliable and, therefore, admissible:
1) is the evidence based on a testable theory or technique;
2) has the theory or technique been peer reviewed;
3) in the case of a particular technique, does it have a known error rate and standards controlling the techniques operation; and
4) is the underlying science generally accepted?
The Court cautioned that the list should not be regarded by judges as “a definitive checklist or test,” opening the door for judges to employ criteria of their own