Expert opinions admitted by courts are not always valid and reliable. However, we know little about how indicators of opinion quality affect the persuasiveness of an expert. In this study 25 Australian magistrates and 22 jury-eligible lay people rated the persuasiveness (via credibility, value and weight) of either a high- or a low-quality expert opinion. Opinion quality was determined using attributes specified in the Expert Persuasion Expectancy (ExPEx) framework: Field, Specialty, Ability and Trustworthiness. Both magistrates and jurors were significantly more persuaded by the high- than the low-quality expert opinion. Magistrates were also significantly more sceptical of the expert opinion than lay people, and when given the opportunity sought information that was logically relevant to their decision. These results suggest that magistrates can differentiate between high- and low-quality expert opinions, but it is unclear whether the information they need for the task is actually available for use during trials.
Keywords: expert evidence; expert testimony; forensic science; judges; jury decision-making; persuasion.
© 2020 The Australian and New Zealand Association of Psychiatry, Psychology and Law.