Friday, October 2, 2009

Science vs law in evaluating expert scientific testimony: From Vidal (2007) Atkins decision

Science vs law in the court room.

I've been skimming the CA Supreme Court Vidal (2007) Atkins-related decision and found a fascinating discussion of the distinction between science and law (thanks to In the News Blog for directing my focus to this section).  For those who don't want to read the entire PDF document previously posted, below is the relevant text.  Professionals who testify (or who are considering testifying) in Atkins cases, should be aware of the courts role in mediating/deciding expert-testimony based scientific debates.  Scientific debates in the court room are not the same as debates between scholars at conferences, in journal articles, etc.

Underlined/italics in the text below reflect the blogmasters emphasis.
In assessing the role the Full Scale IQ score (or any other single test score) plays in determining mental retardation, we must distinguish between rules of law and diagnostic criteria of psychology. The expert testimony below included a vigorous scientific debate as to whether Vidal’s Full Scale IQ scores should rule out a diagnosis of mental retardation. While one psychologist, McKinzey, gave his opinion that Full Scale IQ scores are, in all circumstances, the “best measure of general intelligence,” two other psychologists, Couture and Widaman, testified that where testing showed an extraordinarily wide divergence between Performance and Verbal IQ scores, the Full Scale measure was not a fully reliable measure. In support of their views, both sides gave scientific, not legal, reasons and cited scientific, not legal, authority

The Court of Appeal sided squarely with McKinzey in this debate over psychological standards, stating flatly that “general intellectual functioning is primarily determined by the defendant’s FSIQ score.” Like the psychologists who testified at the hearing, the lower court majority cited scientific sources (references published by the American Psychiatric Association and the American Association on Mental Retardation) rather than legal authority in support of its view. The Court of Appeal majority erred in thus purporting to resolve a factual question--the best scientific measure of intellectual functioning--as a matter of law. In finding the facts of a particular case, courts and juries untrained in science are sometimes called upon to resolve contested scientific issues, but such factual findings do not establish generally applicable rules of law. The superior court here, for example, found on the basis of Couture’s and Widaman’s testimony that in Vidal’s case his Full Scale IQ scores in the low average to average range did not preclude a finding of mental retardation. In a given case an appellate court might, within its proper role, hold that such a finding was not supported by substantial evidence in the hearing record. But an appellate court cannot convert a disputed factual assertion into a rule of law simply by labeling it a “legal standard,” as the Court of Appeal purported to do here.

Courts also must sometimes evaluate disputed scientific assertions in the course of determining the admissibility of expert scientific testimony. In determining the evidentiary reliability of a new scientific technique, California courts look primarily to the technique’s general acceptance in the relevant scientific community, an approach designed to ensure “ ‘that those most qualified to assess the general validity of a scientific method will have the determinative voice.’ ”(People v. Kelly (1976) 17 Cal.3d 24, 31, italics omitted.) Even under the arguably more searching federal court inquiry described in Daubert v. Merrell Dow Pharmaceuticals, Inc. (1993) 509 U.S. 579, “the focus, of course, must be solely on principles and methodology, not on the conclusions that they generate.” (Id. at p. 595.) The courts’ evidentiary gatekeeping function is thus not a warrant for judicial intervention in genuine scientific debates over substantive principles. In any event, we are not faced here with a question of admissibility of disputed evidence but with the question whether, when both sides of a scientific dispute have been presented by expert testimony, an appellate court may declare the debate’s winner as a matter of law.

The Legislature has mandated that trial courts, in determining mental retardation for Atkins purposes (Atkins, supra, 536 U.S. 304), find whether the individual’s “general intellectual functioning” is significantly impaired (§ 1376, subd. (a)), but has not defined that phrase or mandated primacy for any particular measure of intellectual functioning. The question of how best to measure intellectual functioning in a given case is thus one of fact to be resolved in each case on the evidence, not by appellate promulgation of a new legal rule.

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