Risk assessment communication difficulties: An empirical examination of the effects of categorical versus probabilistic risk communication in sexually violent predator decisions

Expert testimony concerning risk and its communication to the trier of fact has important implications for some of the most significant legal decisions. In a simulated sexual violent predator hearing, we examined how mock jurors interpret and use recidivism risk expert testimony communicated either categorically, using verbal labels, or probabilistically, using numeric values. Based upon the STATIC-99R, we compared mock jurors' decision-making and verdicts when we manipulated the style of risk communication across four different risk levels. In terms of verdict decisions, we found that higher risk levels were associated with more commitment decisions, but that this relationship only existed for the categorical risk-communication format. We also replicated previous research demonstrating that participants overestimate recidivism risk in general, especially when higher risk is communicated categorically. Finally, our participants did not differentiate well between the four levels of risk offered, instead apparently employing a more simplistic dichotomy between low or high risk for both their verdict decisions and their thresholds for commitment. The legal and policy implications of our findings are discussed, as well as suggestions for more effective presentation of expert risk testimony.