Stability of the interpretative risk percentages for the RRASOR and Static-99

Current procedures to estimate sex offender recidivism risk typically involve actuarial instruments, either alone or in combination with adjustments based on other considerations. Two of the most commonly employed actuarial instruments for the assessment of sexual recidivism risk are the Rapid Risk Assessment for Sex Offender Recidivism (RRASOR; R. K. Hanson, 1997) and the Static-99 (R. K. Hanson & D. Thornton, 2000). Although multiple studies of the interrater reliability and predictive validity of these instruments have been completed, with very supportive results, there have to date not been any studies of the degree to which the specific risk percentages attached to each instrument's score replicate and remain stable despite changes in underlying samples' recidivism base rates. This study, using data from multiple sources, investigated this issue. The findings indicated that the 5-year risk percentages for the RRASOR were replicated and were remarkably stable despite changes in the sample's underlying recidivism base rate. The Static-99 5-year risk percentages were mostly replicated and were stable across varying base rates, but to a lesser degree than was found for the RRASOR. Implications of these results are discussed.