The effect of a peer-led problem-support mentor intervention on self-harm and violence in prison: An interrupted time series analysis using routinely collected prison data

Background: Levels of mental disorder, self-harm and violent behaviour are higher in prisons than in the community. The purpose of this study was to determine whether a brief peer-led problem-support mentor intervention could reduce the incidence of self-harm and violence in an English prison. Methods: An existing intervention was adapted using a theory of change model and eligible prisoners were trained to become problem-support mentors. Delivery of the intervention took two forms: (i) promotion of the intervention to fellow prisoners, offering support and raising awareness of the intervention but not delivering the skills and (ii) delivery of the problem-solving therapy skills to selected individual prisoners. Training and intervention adherence was measured using mentor log books. We used an Interrupted Time Series (ITS) design utilizing prison data over a 31 month period. Three ITS models and sensitivity analyses were used to address the impact across the whole prison and in the two groups by intervention delivery. Outcomes included self-harm and violent behaviour. Routine data were collected at monthly intervals 16 months pre-, 10 months during and six months post-intervention. Qualitative data measured the acceptability, feasibility, impact and sustainability of the intervention. A matched case-control study followed people after release to assess the feasibility of formal evaluation of the impact on re-offending up to 16 months. Findings: Our causal map identified that mental health and wellbeing in the prison were associated with environmental and social factors. We found a significant reduction in the incidence of self-harm for those receiving the full problem-solving therapy skills. No significant reduction was found for incidence of violent behaviour. Interpretation: Universal prison-wide strategies should consider a series of multi-level interventions to address mental health and well-being in prisons.