Recidivism and Static-99R risk assessments in a Swedish cohort of mentally disordered sexual offenders

Abstract

Mentally disordered sexual offenders (MDSOs) constitute a heterogeneous offender subgroup presenting a wide range of clinical comorbidity. The recidivism rates for such a disparate subgroup vary substantially, which complicates estimations of recidivism risk. The commonly used risk assessment instrument Static-99R has been tested on MDSOs, but it is uncertain how it performs in a Swedish population. The aims of this thesis were to (1) present a Swedish cohort of MDSOs in detail regarding cohort characteristics and recidivism pattern over approximately 20 years of follow-up, (2) examine the predictive qualities of the Static-99R in the cohort, and (3) analyze the psychometric properties of the Static-99R using modern test theory. The cohort comprised 146 convicted adult male sexual offenders who underwent a forensic psychiatric investigation (FPI) as part of their legal process in Sweden between 1993 and 1997. Data were collected from official registries, written court documents, and the FPI reports. Prevalence rates for major mental illnesses were substantial, and most were previously convicted—one third for prior sexual offenses. Half were reconvicted over the follow-up period, though primarily for non-sexual offenses. Recidivism rates for sexual offenses were 9.6% after 5 years, 13.0% after 10 years, 15.1% after 15 years, and 17.1% after 20 years. Recidivism was primarily clustered around the first 5 years after the index offense, with an average of 6.5 years until first new sexual or violent offense. Static-99R performed adequately over 5–20 years of fixed follow-up after release (AUC .73-.79) and the cohort was most similar to the “routine sample” norms when estimating recidivism risk, although with 30% fewer recidivists predicted than expected across all risk categories. The Static-99R demonstrated several psychometric issues, in particular items 1, 3 and 5. This was improved by experimenting with fewer response categories for items 1 and 5, and the exclusion of item 3. In conclusion, the cohort of MDSOs demonstrated internationally comparable recidivism rates as well as high rates of major mental illness. Additionally, the Static-99R may be administered to MDSOs in Sweden, using the “routine sample” norms when estimating recidivism risk, and items 1, 3, and 5 may merit highlighting in future revisions of the instrument concerning this particular subgroup.