By Dr. Ken Broda-Bahm:
It is common experience that jurors will often set aside expert testimony. Part of it, of course, is a "hired gun" effect that in some cases leads jurors to distrust experts based on the knowledge that they've been paid for their opinions by one side or the other. But over time, I've come to believe that is not the dominant reason jurors have for avoiding reliance on experts. Instead, there is a more basic reason at work: Jurors don't use experts because they're not convinced they need experts. They think they know the general idea well enough already. Why listen to a product safety expert if I think product dangers are obvious based on common sense? Why listen to a construction expert if I have a brother-in-law who works in construction?
This overconfidence and preference for personal knowledge has a social science name: the illusion of explanatory depth. It's a cognitive bias that occurs when people believe they understand a concept more fully and more specifically than they actually do. The way it works is this: Once we're able to appreciate or articulate something at a very general or abstract level, we come to believe that we understand the specifics and the mechanics of it at a concrete level as well. But, we don't. As one of the most comprehensive recent studies of the phenomenon (Alter, Oppenheimer & Zemla, 2010) has noted, this perceived general understanding isn't something we can trust. "Although folk wisdom suggests that people often fail to see the forest for the trees," the authors note, "sometimes the greater concern is that people fail to see the trees for the forest." That has an immediate relevance to jurors' and other fact finder's understanding of expert testimony. Jurors can fall victim to overconfidence in understanding, and the experts themselves can unwittingly promote that illusion. The main goal is to avoid abstract explanations and be concrete instead. In order to practice what I preach, I mean to concretely explain in this post what I mean by "be concrete."