VIOLENT RECIDIVISM - ASSESSING PREDICTIVE-VALIDITY

Until very recently, there has been little evidence of the ability of either clinicians or actuarial instruments to predict violent behavior. Moreover, a confusing variety of measures have been proposed for the evaluation of the accuracy of predictions. This report demonstrates that receiver operating characteristics (ROCs) have advantages over other measures inasmuch as they are simultaneously independent of the base rate for violence in the populations studied and of the particular cutoff score chosen to classify cases as likely to be violent. In an illustration of the value of this approach, the base rates of violence were altered with the use of data from 3.5-, 6-, and 10-year follow-ups of 799 previously violent men. Base rates for the 10-year follow-up were also altered by changing the definition of violent recidivism and by examining a high-risk subgroup. The report also shows how ROC methods can be used to compare the performance of different instruments for the prediction of violence. The report illustrates how ROCs facilitate decisions about whether, at a particular base rate, the use of a prediction instrument is warranted. Finally, some of the limitations of ROCs are outlined, and some cautionary remarks are made with regard to their use.