The effect of clinical vs. scientific expert testimony on mock juror decision-making in capital sentencing

Abstract

The Supreme Court and many state courts have assumed that jurors are capable, with the aid of adversary procedures (i.e., cross-examination and competing experts), of differentiating less accurate clinical opinion expert testimony (testimony based solely on a clinician's years of experience within the field) from expert testimony based on more sound scientific footing, and appropriately weighing these two types of testimony in their decisions. Psychological literature on both persuasion and jury decision-making suggests, however, that this assumption is dubious. Using a simulated capital sentencing hearing based on Texas law, this experiment investigated whether mock jurors are more influenced in their decision-making by clinical opinion expert testimony or actuarial expert testimony (testimony based on standardized risk assessment instrument). The effectiveness of different types of adversary procedures in eliminating the influence of expert testimony was also investigated. Results suggest that jurors are more influenced by clinical opinion expert testimony than they are by actuarial expert testimony, and this preference for clinical opinion expert testimony remains even after the presentation of adversary procedures. Limited empirical support was found for the notion that various types of adversary procedures will have differential impact on the influence of expert testimony on juror decisions. The legal and policy implications of these findings are discussed.