Prediction of violent reoffending in people released from prison in England: External validation study of a risk assessment tool (OxRec)

Abstract

We aimed to externally validate the Oxford Risk of Recidivism (OxRec) tool to estimate 1- and 2-year risk of violent reoffending in people released from prison in England. We identified individuals using admiistrative data shared between official prison and police services. We extracted information on criminal history, clinical and sociodemographic risk predictors, and outcomes. Predictive ability was examined using measures of calibration and discrimination for predetermined risk thresholds. In total, 1770 individuals (median age = 33 [IQR 27–40]; 92% were male) were identified. 31% and 43% reoffended within 1 and 2 years, respectively. Discrimination was good, with AUCs of 0.71 (95% CI: 0.69-0.74) for 1 year and 0.71 (0.68-0.74) for 2-year follow up. At a pre-specified threshold of 40% for 2-year risk, sensitivity was 77% (74%–80%), specificity 54% (51%–58%), PPV 56% (53%–59%) and NPV 76% (73%–79%). Simple model validation found a systematic underestimation of the probability of reoffending. However, after updating the model, calibration was good. External validations of risk assessment tools can be conducted using linked data between prison and police, and may require recalibration before implementation. In this validation, OxRec had good performance on discrimination and calibration measures. It can be considered to be used to improve decision-making about risk of serious offending and the allocation of resources.