An open access publication of the American Academy of Arts & Sciences
Fall 2018

Improving Judge & Jury Evaluation of Scientific Evidence

Valerie P. Hans and Michael J. Saks

The role of the expert witness in trials is a paradox. Judges and jurors need help with matters beyond their understanding, and judges are expected to act as gatekeepers to ensure that jurors are not fooled by misleading expert testimony. Yet, as gatekeepers, judges might not effectively distinguish sound from unsound expert testimony. As factfinders, judges and jurors both might have difficulty comprehending expert evidence, intelligently resolving conflicts between experts, and applying the scientific and technological evidence they hear to the larger dispute before them. This essay explores those problems and a variety of possible solutions, ranging from more effective ways parties might present technical information at trial, to educational interventions supervised by the court, to making juries more effective in performing their task, to more controversial measures, such as replacing conventional juries with special juries and replacing generalist judges with expert judges.

VALERIE P. HANS is Professor of Law at Cornell Law School. She is the author of The Psychology of Tort Law (with Jennifer K. Robbennolt, 2016), American Juries: The Verdict (with Neil Vidmar, 2007), and Business on Trial: The Civil Jury and Corporate Responsibility (2000).

MICHAEL J. SAKS is Regents Professor at Arizona State University, where he is on the faculties of the Sandra Day O'Connor College of Law and the Department of Psychology. He is the author of The Psychological Foundations of Evidence Law (with Barbara A. Spellman, 2016) and author/editor of Modern Scientific Evidence: The Law and Science of Expert Testimony (with David L. Faigman, Joseph Sanders, and Edward K. Cheng, 2009–2010).

The fundamental paradox of the use of expert evidence in litigation is that those with the power and duty to evaluate expert testimony possess less knowledge of the specialized subject matter at issue than do the experts whose testimony they are evaluating. Judges experience this paradox not only when they are performing as factfinders in bench trials, but also when they are acting as gatekeepers of expert testimony. As one prominent judge observed:

Though we are largely untrained in science and certainly no match for any of the witnesses whose testimony we are reviewing, it is our responsibility to … resolve disputes among respected, well-credentialed scientists about matters squarely within their expertise, in areas where there is no scientific consensus.1

The paradox also exists for juries. As Judge Learned Hand asked in 1901, “How can the jury judge between two statements each founded upon an experience confessedly foreign in kind to their own? It is just because they are incompetent for such a task that the expert is necessary at all.”2 .  .  .


  • 1Daubert v. Merrell Dow Pharmaceuticals, Inc., 43 F.3d 1311, 1316 (1995). The common law allowed expert evidence to be introduced only when the expert was testifying to matters beyond the ken of the average juror. This requirement was incorporated into Federal Evidence Rule 702, which allowed for expert evidence in circumstances in which the knowledge would assist the trier of fact in understanding the evidence or determining a fact in issue.
  • 2Learned Hand, “Historical and Practical Considerations Regarding Expert Testimony,” Harvard Law Review 15 (1) (1901): 54.
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