Characterizing the value of actuarial violence risk assessments

Using the Violence Risk Appraisal Guide, relative operating characteristic (ROC) statistics are exemplified. Criticisms of actuarials and ROCs as measures of accuracy are discussed-ROC statistics are independent of base rates, but optimal decisions are not. Using sex offenders, the importance of accurate base rate information in the relevant population is examined. Although Bayes affords estimates of posterior probabilities for any base rate, Bayesian corrections can be too extreme in practice. This article illustrates that undesirable posterior probabilities are improved by superior selection ratios and refutes the criticism that "confidence intervals around individual scores" are so large as to make actuarial assessment meaningless. Personal values play a role in forensic decision making, and actuarial methods sharpen the focus on such values.