Effects of psychopathy and violence risk testimony on mock juror perceptions of dangerousness in a capital murder trial

The recent introduction of the Psychopathy Checklist-Revised (PCL-R) into the sentencing phase of capital murder trials has heightened concerns about the potentially prejudicial impact of such information on jurors, who might give disproportionate weight to this diagnosis when determining whether a defendant is a "continuing threat to society". To investigate this issue, 238 undergraduates read a case summary based on US v. Barnette (2000), in which prosecution testimony was presented regarding the presence of a mental disorder (psychopathy, psychosis, or no disorder). Compared to the "no disorder" condition, participants rated psychopathic defendants as more likely to be violent in the future, even though testimony related to level of risk (high or low) was held constant. The difference in perceived dangerousness across the psychopathy and no disorder groups was particularly pronounced when the experts described the defendant as being at low risk. A similar pattern of effects was noted for the psychosis condition, suggesting that the impact of mental disorder testimony on perceptions of dangerousness may not necessarily be specific to the PCL-R.