Improving risk assessment in forensic mental health: temporal validation and clinical refinement of the FoVOx risk tool

Background: Forensic psychiatric services are expanding in many countries, and discharging patients from secure hospitals relies on accurate estimates of risk of adverse outcomes.Novel evidence-based tools for estimating one key risk, violent reoffending, have been developed in recent years.We aimed to externally validate one new tool, FoVOx, in forensic psychiatric patients sentenced to treatment, and to develop an updated model (FoVOx2), incorporating additional clinical predictors.Methods: Using Swedish national registers, we conducted a temporal external validation of FoVOx by examining 767 patients discharged between 2014 and 2023.For the FoVOx2 cohort, 906 patients discharged between 2008 and 2023 were followed up, and additional predictors tested.The outcome was violent reconviction within 12 or 24 months.Model performance was evaluated using Harrell's C-index, time-dependent AUCs, calibration, and classification metrics at predefined thresholds.Results: In temporal validation, FoVOx showed moderate discrimination (AUCs 0.69 and 0.71; C-index = 0.69) and acceptable overall accuracy (Brier <0.11).Calibration was generally good, with mild overestimation at the highest predicted risks (>20%) at 12 months and slight underprediction at 24 months.The updated FoVOx2 model newly incorporated clozapine treatment and additional diagnostic categories.It was associated with improved performance (AUCs 0.77; optimism-corrected C-index = 0.72; Brier 0.06 and 0.09) and achieved good calibration (intercept 0; slopes 1.03 and 1.05).