Optimal threshold for static 99R

Abstract

The Static 99R is an actuarial instrument that is widely used to assess the sexual recidivism risk of sex offenders. It is frequently applied in jurisdictions as a decision-making tool for release or indefinite admission to a psychiatric hospital within the jail of sex offenders. The decision to release or retain a criminal depends solely on the total score which is considered as the only independent variable. In our study, two models of Static 99R are considered: the 5-year high risk model and the 10-year high risk model. To identify the most appropriate threshold, we performed four independent methods. These are: the point closest-to-(0,1), the concordance probability (CZ), the index of union (IU), and the plot of sensitivity versus specificity. Remarkably, all four methods yielded identical results. For the 5-year high risk model, the optimal threshold is 0.184, which corresponds to a cut-off score of 5. Consequently, a score of 5 or higher implies that the offender is very likely to recidivate. Similarly, for the 10-year high risk, the optimal threshold is 0.293 which corresponds also to a cut-off score of 5.

Predictive and incremental validity of the Static-99, Static-99R, and STABLE-2007 for sexual recidivism: A diagnostic test accuracy network meta-analysis (DTA-NMA).

“…Our findings indicate that the Static-99R offers higher predictive validity than the Static-99 for sexual recidivism. Its optimal cutoff was identified at “above average [IVa]” (corresponding to raw scores 4–5), which is in line with the findings of previous work (Baudin et al, 2021; Chang et al, 2023; Gonçalves et al, 2020). According to the coding guideline, raw scores of 4–5 are thought to separate individuals convicted of sexual offenses “in the middle of the risk distribution” from those demonstrating “perceptibly higher risk” (Phenix, Helmus, et al, 2016, p. 4).…”

“…In a second study, based on 146 male individuals from Sweden across 5- and 20-year follow-up periods, a slightly higher cutoff at the raw score of 6 for the Static-99R (well above average [IVb]) was observed; however, the difference from the raw score of 4 (above average [IVa]) was described as negligible (Baudin et al, 2021). The third study (Chang et al, 2023), based on 860 and 359 adult males across 5- and 10-year follow-up periods (Phenix, Fernandez, et al, 2016), noted the optimal cutoff at the raw score of 5 for the Static-99R (above average [IVa]). These three studies provided the first estimates of risk levels that may best discriminate recidivists from nonrecidivists.…”