Background: The dangerous severe personality disorder programme was developed in high secure prisons and hospitals at great expense to identify and treat the most dangerous offenders with personality disorders.
Aims: To evaluate whether the long-term costs of the programme are greater or less than the long-term outcomes.
Method: We used a Markov decision model with a cost-effectiveness analysis to determine the incremental cost of the programme per serious offence prevented and a cost-offset analysis to consider whether monetary benefits were greater than costs.
Results: Costs were consistently higher for the intervention programme and the cost per serious offence prevented was over £2 million, although there was some evidence that adjustments to the programme could lead to similar interventions becoming cost-effective.
Conclusions: Little evidence was found to support the cost-effectiveness of the intervention programme for offenders with personality disorders, although delivery of the programme in a lower-cost prison would probably yield greater benefits than costs. There are frequent calls for mentally disordered offenders to be detained in secure hospitals rather than prisons; however, if reoffending remains the outcome of interest for policy makers, it is likely that the costs of detention in hospital will remain greater than the benefits for dangerous offenders with a personality disorder.