Updating Probability in Sex Offender Risk Assessment

Abstract

Actuarial scales like the Static-99R are widely used to predict an individual’s risk of sexual recidivism. However, current actuarial scales only provide rates of detected sex offenses over 10-year follow-up and do not account for all recidivism risk factors. Therefore, some forensic evaluators extrapolate, adjust, or override recidivism rates derived from actuarial scales to predict the lifetime risk of committed offenses that accounts for external risk factors, those not addressed by the actuarial scales. However, critics contend that altering rates from actuarial scales degrades their predictive validity. This article makes the case for extrapolating risk for time of exposure and for evidence-based external risk factors. It proposes using odds ratios (ORs) from case-control studies to adjust predictions from follow-up cohort studies. Finally, it shows how evaluators can apply ORs and their margins of error to sex offender risk assessment.