Developing programme theories to address unmet needs of people experiencing homelessness and severe mental illness: protocol for a realist review

<ns3:p>Introduction People experiencing both homelessness and severe mental illness have complex needs requiring coordinated multi-sectoral and multilevel interventions. Several systematic reviews of interventions exist internationally; however, evidence on the mechanism of change and contextual factors is limited. The proposed realist review aims to synthesize evidence to understand what interventions work, how, why, for whom, and under what circumstances in low and middle-income country settings. Methods This work is nested within the National Institute for Health and Care Research (NIHR) Global Health Research Group on Homelessness and Mental Health in Africa (HOPE) project in Ethiopia, Ghana, and Kenya. In HOPE, we use participatory methods to develop and evaluate community-based interventions to address the unmet needs of people who are homeless and have severe mental illness living in the three countries. This protocol details the methodology for a realist review to inform the development, testing, and refinement of a programme theory for intervention. The review will follow five iterative steps. Step 1: Clarify the review scope and develop initial programme theories (IPTs). Step 2: Search for evidence across electronic databases and hand search for published studies to test and refine the IPTs. Step 3: Select and appraise studies. Step 4: Extract data, Step 5: Analyse and synthesize extracted data. The IPTs will be supplemented with formal theories to enhance their explanatory power. Key stakeholders will give critical inputs throughout the review process. Discussion The findings of the realist review will inform the development of contextually relevant programme theories to address the unmet needs of people who are homeless and have severe mental illness in LMICs, which will then be tested and refined within a realist evaluation. PROSPERO registration: CRD420251067136</ns3:p>