Abstract
Scalable and transparent methods for risk assessment are increasingly required in criminal justice to inform decisions about sentencing, release, parole, and probation. However, few such approaches exist and their validation in external settings is typically lacking. A total national sample of all offenders (9072 released from prisoners and 6329 individuals on probation) from 2011–2012 in the Netherlands were followed up for violent and any reoffending over 2 years. The sample was mostly male (n = 574 [6%] were female prisoners and n = 784 [12%] were female probationers), and median ages were 30 in the prison sample and 34 in those on probation. Predictors for a scalable risk assessment tool (OxRec) were extracted from a routinely collected dataset used by criminal justice agencies, and outcomes from official criminal registers. OxRec’s predictive performance in terms of discrimination and calibration was tested. Reoffending rates in the Dutch prisoner cohort were 16% for 2-year violent reoffending and 44% for 2-year any reoffending, with lower rates in the probation sample. Discrimination as measured by the c-index was moderate, at 0.68 (95% CI: 0.66–0.70) for 2-year violent reoffending in prisoners and between 0.65 and 0.68 for other outcomes and the probation sample. The model required recalibration, after which calibration performance was adequate (e.g. calibration in the large was 1.0 for all scenarios). A recalibrated model for OxRec can be used in the Netherlands for individuals released from prison and individuals on probation to stratify their risk of future violent and any reoffending. The approach that we outline can be considered for external validations of criminal justice and clinical risk models.
Highlights
Risk assessment tools in criminal justice, forensic mental health, and clinical psychiatry are increasingly used to stratify individuals into different categories based on their predicted future risk of crime and violence
Of the strongest risk factors may not be modifiable in the way that criminogenic needs are usually considered, and some needs may not be associated with reoffending risk
One tool in criminal justice that follows these methods is the Oxford Risk of Recidivism Tool, OxRec[10]. It was developed and externally validated in Sweden using a total population of prisoners, and provides both a probability score for violent reoffending and stratifies according to prespecified low, medium and high categories. It represents a considerable advance in criminal justice because it takes around 10–15 minutes to complete, relies on mostly routinely collected information, has an online calculator that can be used freely by mental health and criminal justice professionals, does not require any formal training, and performs as well as current approaches to risk assessment in criminal justice that take many hours[16]
Summary
Data from risk assessments performed in 2011 and 2012 were available for 9072 prisoners and 6329 non-prisoners. As the reoffending rate was lower than in the Swedish cohort (Supplementary Table 2), the predicted numbers of outcome events using the uncalibrated OxRec were much higher than the numbers that were observed in the Dutch sample (Supplementary Table 3), which meant that the calibration using the existing OxRec tool was suboptimal This was apparent for all outcomes, but was pronounced for those in non-prisoners, for whom the incidence of reoffending was much lower (Supplementary Table 2). Model performance is expressed in relation to thresholds to define medium and high risk After recalibration, these were set as 10% and 30% (respectively) for 2-year violent reoffending, and 30% and 50% (respectively) for 2-year any reoffending (Table 2)
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