A respecification of Hanson's updated Static-99 experience table that controls for the effects of age on sexual recidivism among young offenders

Abstract

The original version of Static-99 is widely used for assessing sexual recidivism. It does not, however, account for the negative effect of age on recidivism. Hanson (2006, Sexual Abuse, 18, 343-355) took up this problem by disseminating an updated experience table for Static-99, based on 3425 sex offenders, that was stratified by four rows of risk categories and five columns of age categories. Contrary to expectations, updated Static-99 reported that the highest group-wise recidivism rates accrued to sex offenders in the second youngest category. The explanation for this inconsistency is that the entries in updated Static-99 are misspecified for the youngest offenders because, in effect, Hanson used one scoring system for assigning older offenders to risk groups and another for the classification of younger offenders. Updated Static-99, therefore, needs to be respecified. We applied a Bayesian algorithm to do so. Updated Static-99 holds out so many advantages that we believe it is unethical for evaluators to use original Static-99 unless they can present overwhelming evidence in support of this choice. Other contributions of respecifying updated Static-99 are discussed.