Standards of evidentiary reliability

Federal Rule of Evidence 702, and its variations adopted by most states, defines the admissibility of expert testimony in the following manner: 

If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise (Melton, Petrila, Poythress, & Slobogin,1997,p.16).

Since 1923, Frye v. US has served as the standard for determining whether an expert's testimony would "assist the trier of fact." Frye required that expert testimony be supported by scientific principles or evidence generally accepted by the relevant scientific or professional community. Frye rulings traditionally relied on peer review, particularly the availability of peer-reviewed articles, to assess general acceptance.

In 1993, the US Supreme Court's decision in Daubert v. Merrell Dow Pharmaceuticals, Inc. superseded Frye in federal courts. Daubert defines a four-prong test for determining the "evidentiary reliability" of a scientific theory or technique:

More recently, the US Supreme Court's 1999 decision in Kumho Tire, Inc. v. Carmichael further expanded the reach of Daubert. In his majority opinion, Justice Breyer wrote that a trial judge must determine whether proposed expert testimony that "reflects scientific, technical or other specialized knowledge" has a "reliable basis in the knowledge and experience of [the relevant] discipline" (Wierner, 1999, p. 47)

Whereas various courts previously ruled that Daubert was applicable only to the procedures of a laboratory science, and therefore not applicable to clinical opinion, Kumho extends Daubert to opinion testimony.

State courts are not obligated to adopt how federal courts interpret rules of evidence. Consequently, there is considerable variation between states regarding criteria for defining the admissibility of expert testimony. During the first two years after the Daubert ruling, 11 states adopted it, and five rejected it (melton et al., 1997). Assessing the evidentiary reliability of the instruments used for sexual

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predator evaluations therefore necessitates considering both Frye and Daubert (as further defined by Kumho).

Pursuant to Frye, any assessment instrument that has not gained general acceptance, typically via peer review, would be considered an experimental instrument. General acceptance -- as opposed to status as an experimental instrument -- also necessitates that a procedure satisfy relevant practice and ethical standards.

Frye criteria would prohibit an expert from relying on an experimental instrument while testifying in a legal proceeding. In addition to peer review and related considerations of general acceptance, Daubert would reject any assessment instrument

Assessment instruments that fail to satisfy these Daubert criteria can also be considered as remaining at an experimental stage of development. 

Relatedly, Rogers, Salekin, and Sewell (1999) have indicated that many commonly used psychological tests may not satisfy standards of evidentiary reliability in legal proceedings.
In particular, they stated:

Within a larger framework , we envision the need to re-evaluate systematically commonly used psychological tests and measures in light of the Daubert standard. As observed in post-Daubert decisions, appellate courts rely on the professional literature in their determinations of falsifiability, error rate, and scientific acceptability of psychological tests.
Systematic reviews a la Daubert may address either general issues of diagnostic validity or focus specifically on psycho-legal constructs (e.g., competency to stand trial). Such scholarly efforts will assist both forensic psychologists in selecting psychological measures and the trial courts in determining their acceptability (p. 440).

Quite clearly, there is no acceptable rationale for exempting risk assessment procedures from the issues raised by Rogers et al. (1999). Indeed, there is a compelling need for systematically reviewing the instruments currently used for risk assessment in cases of previously convicted sexual offenders.