The interesting study, just published in the International Journal of Offender Therapy and Comparative Criminology, was designed to validate German versions of commonly used actuarial tools, including the Static-99, RRASOR, SORAG, and SVR-20. It followed about 400 Austrian prisoners for an average of three years in the community.
The main problem obtaining significant results was that recidivism was so rare. Obviously, the less likely an event is to occur, the harder it is to accurately predict. Only seven offenders in the entire sample committed a new hands-on offense during the followup period, and most of those were extrafamilial child molesters. Recidivism base rates were especially low for rapists and incest offenders.
The results echoed findings in two other recent studies in which the actuarials failed to demonstrate good predictive validity for predicting sexually violent reoffending.
Most of the instruments did better when recidivism was defined more broadly, to include all sexual reconviction, even hands-off offenses such as voyeurism or exhibitionism that is not typically defined as sexually violent under civil commitment laws. Even including these lesser offenses, the overall base rate for all sexual recidivism among this sample was still quite low, 4.3% (12% among extrafamilial child molesters, 1.7% among rapists, and about 1% among incest offenders).
When extrafamilial child molesters -- the group most likely to reoffend -- were examined separately, all of the instruments except the RRASOR had some predictive utility, with the SVR-20 doing the best. Still, neither the Static-99 (the most widely used actuarial tool) nor the RRASOR could significantly predict sexually violent reoffenses even for that relatively higher-risk group.
"From the results of these studies and of the present study, the actuarial prediction of some reoffence categories in at least some offender subtypes is less accurate than generally assumed,” the authors concluded. "One major aim of most criminal justice systems is to calculate risk by predicting the probability of severe sexual crimes. This goal obviously is not yet achieved satisfactorily by actuarial risk assessment, because results are far from ideal, especially when time-at-risk periods are relatively short."
An important implication of this study is that evaluators need to consider offender subgroups separately, rather than lumping all types of sex offenders together. Recidivism varies tremendously by type of offender (e.g., rapists versus child molesters) and by how recidivism is defined, with the various instruments doing better at some types of predictions than others. Furthermore, so little outcome research exists on certain groups (such as hands-off offenders, juveniles, the intellectually disabled, and offenders with only adult male victims) that the actuarials may be inappropriate to use at all.
The study is:
Rettenberger, M., Matthes, A., Boer, D.P., & Eher, R. (2010). Prospective Actuarial Risk Assessment: A Comparison of Five Risk Assessment Instruments in Different Sexual Offender Subtypes. International Journal of Offender Therapy and Comparative Criminology, 54 , 169-186.
Hat tip: Jeffrey Singer
FURTHER READING: For those of you interested in the actuarials, I also recommend "More prejudicial than probative?," a stastical critique by David J. Cooke, a forensic psychology professor in Glasgow who is an expert scholar and trainer on violence risk assessment. Cooke argues that the actuarials are compelling because they are simple to use by paraprofessionals and have a scientific veneer, but "the scientific basis for actuarial scales, as applied to individuals, may be more illusory than real." The article, in the journal of the Law Society of Scotland, is available online. It also includes useful references to other sources.