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 t hat receiver operating characteristics (ROCs) have advantages over oth er measures inasmuch as they are simultaneously independent of the bas e rate for violence in the populations studied and of the particular c utoff score chosen to classify cases as likely to be violent. In an il lustration of the value of this approach, the base rates of violence w ere 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 w ere also altered by changing the definition of violent recidivism and by examining a high-risk subgroup. The report also shows how ROC metho ds can be used to compare the performance of different instruments for the prediction of violence. The report illustrates how ROCs facilitat e decisions about whether, at a particular base rate, the use of a pre diction instrument is warranted. Finally, some of the limitations of R OCs are outlined, and some cautionary remarks are made with regard to their use.