The Prejudices of Expert Evidence

The rules and procedures regulating the admission of potentially unreliable expert evidence have been substantially weakened over the past several years. We respond to this trend by focusing on one aspect of the rules that has not been explicitly curtailed: unfair prejudice. Unfair prejudice is an important component of trial judges’ authority to exclude evidence, which they may do when that unfair prejudice outweighs the evidence’s probative value. We develop the concept of unfair prejudice by first examining how it has been interpreted by judges and then relating that to the relevant social scientific research on the characteristics of expertise that can make it prejudicial. In doing so, we also discuss the research behind a common reason that judges admit expert evidence despite its prejudice, which is that judicial directions help jurors understand and weigh it. As a result, this article provides two main contributions. First, it advances knowledge about unfair prejudice, which is an important part of expert evidence law that has received relatively little attention from legal researchers. Second, it provides guidance to practitioners for challenging expert evidence under one of the few avenues left to do so.