The Ethos of Expert Witnesses: Confusing the Admissibility, Sufficiency and Credibility of Expert Testimony

Eileen A. Scallen, William Mitchell College of Law

This article is co-authored by William E. Wiethoff, Attorney, Bloomington, Indiana (Ph.D. Speech, University of Michigan)


This article focuses on a problem that is presented by expert testimony, and how that problem is best addressed. The article argues that the problem of expert testimony cannot be resolved adequately simply by turning judges into amateur scientists but that the problem must be confronted at its core: Science and law speak different languages. A judge, even one trained in the scientific method, cannot along translate the testimony of expert witnesses into meaningful legal discourse. Further, the article notes that while both the judge and the jury have roles in the evaluation of an expert’s ethos, judges have been improperly accorded the dominant responsibility for evaluating the expert’s ethos which obscures the fact that expert testimony is, at bottom, “opinion,” traditionally evaluated by the trier of fact, often a jury. In support of this, the United States Supreme Court’s recent decision in General Electric Co. v. Joiner is used as an example of how a court may confuse the issues of admissibility, sufficiency, and credibility of expert testimony. The article also argues that in order to generate a thoughtful understanding of expert testimony, more careful attention must be paid to actual expert speech, focusing on the objectionable qualities of it. This argument is illustrated by an examination of the expert testimony in the trial of Dan White, who shot and killed San Francisco Mayor George Moscone and San Francisco Supervisor Harvey Milk on November 27, 1978. The expert testimony in this case was the source of one of the trial’s most memorable images and one of the most reviled examples of “junk science” – the “Twinkie defense.” Overall, the article suggests that the best solution is for the judge, experts, advocates, jury, and in some notable cases, the scientific, legal, and general communities to all play their parts to translate expert testimony into an acceptable decision.