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

Abstract

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.

Testing a new non-arbitrary system for risk communication

“…Notwithstanding these aims, there are fundamental barriers in the literature impeding upon clear risk communication. Research has consistently shown both judges and laypeople prefer categorical descriptions of risk despite the fact that categorical communication can lead to an overestimation of risk, leading to higher conviction rates, or harsher sentences (Krauss et al, 2018;Scurich, 2018). Risk communicated in a frequency format (e.g., 1 in 10) has been shown to lead to lower likelihoods of commitment decisions than risk communicated in a probability format (e.g., 10% chance), though both are numerically equal (Slovic et al, 2000).…”

“…Research has also examined the effect of risk communication on laypeople. In a mock Sexually Violent Predator (SVP) commitment hearing, jurors presented with a categorical estimate were more likely to commit 'high risk' individuals than individuals given a probabilistic estimate (e.g., 13% likely to reoffend in 10 years) that equated to a 'high risk' decision on the Static-99R (Krauss et al, 2018). Commitment decisions were found to increase as categorical risk level increased, while these results were not replicated when jurors were presented with probabilistic estimates.…”

“…Commitment decisions were found to increase as categorical risk level increased, while these results were not replicated when jurors were presented with probabilistic estimates. Categorical risk estimates may lead jurors to overestimate risk and therefore be more likely to commit individuals (Krauss et al, 2018). Presenting risk in a probabilistic format may provide the base rates necessary for jurors to make more accurate commitment decisions (Krauss et al, 2018).…”

“…Categorical risk estimates may lead jurors to overestimate risk and therefore be more likely to commit individuals (Krauss et al, 2018). Presenting risk in a probabilistic format may provide the base rates necessary for jurors to make more accurate commitment decisions (Krauss et al, 2018). Scurich (2018) goes further suggesting that risk be solely communicated numerically, as forensic science in general is moving away from categorical statements and estimates.…”

“…The researchers presented risk either categorically (low, low-moderate, moderate-high, high) or probabilistically (13%, 21%, 30%, 43%), consistent with the estimates from the Static-99. SVP commitment decisions increased when assessments contained a categorical risk communication method rather than a numerical (probabilistic) one (Krauss, 2018).…”