LOW BASE RATES LIMIT EXPERT CERTAINTY WHEN CURRENT ACTUARIALS ARE USED TO IDENTIFY SEXUALLY VIOLENT PREDATORS: An Application of Bayes's Theorem

The author applied Bayes's theorem to agewise sexual recidivism rates and the accuracy of high actuarial scores for predicting sexual recidivism in civil commitment cases. Recidivism rates consistently declined with age, paralleling the age-invariance pattern found for other offenders. Furtherm...

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Bibliographic Details
Published in:Psychology, public policy, and law public policy, and law, 2006-02, Vol.12 (1), p.56-85
Main Author: Wollert, Richard
Format: Article
Language:English
Subjects:
Age Differences
Criminal Offenders
Human
Male
Perpetrators
Prediction
Recidivism
Sex Offenses
Statistical Probability
Violence
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Summary:The author applied Bayes's theorem to agewise sexual recidivism rates and the accuracy of high actuarial scores for predicting sexual recidivism in civil commitment cases. Recidivism rates consistently declined with age, paralleling the age-invariance pattern found for other offenders. Furthermore, actuarials were efficient for only the youngest group, were inaccurate for identifying recidivists, and misclassified many nonrecidivists as recidivists. Opinions about the accuracy of actuarials are therefore often wrong, and actuarials need to be reformulated. Finally, actuarials are useless for identifying likely sexual recidivists from populations with recidivism base rates below .25. Recommendations include seeking new trials in cases that overlooked age, focusing attention on young offenders, limiting commitment periods, and shifting resources from commitment centers to impact all offenders released to the community.
ISSN:1076-8971
1939-1528
DOI:10.1037/1076-8971.12.1.56