Differences in expert witness knowledge: do mock jurors notice and does it matter?

The knowledge of experts presumably affects their credibility and the degree to which the trier of fact agrees with them. However, specific effects of demonstrated knowledge are largely unknown. In this experiment, we manipulated a forensic expert's level of knowledge in a mock-trial paradigm. We tested the influence of low versus high expert knowledge on mock juror perceptions of expert credibility, on agreement with the expert, and on sentencing. We also tested expert gender as a potential moderator. Knowledge effects were statistically significant; however, these differences carried little practical utility in predicting mock jurors' ultimate decisions. Contrary to the hypotheses that high knowledge would yield increased credibility and agreement, knowledge manipulations influenced only perceived expert likeability. The low-knowledge expert was perceived as more likeable than the high-knowledge counterpart, a paradoxical finding. No significant differences across expert gender were found. Implications for conceptualizing expert witness knowledge and credibility and their potential effects on juror decision-making are discussed.
(© 2015 American Academy of Psychiatry and the Law.)