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

Homelessness; programme theory; realist approach; severe mental illness ALL Metrics - Views Downloads How to cite this article Abayneh S, Asher L, Smartt C et al. Developing programme theories to address unmet needs of people experiencing homelessness and severe mental illness: protocol for a realist review [version 1; peer review: 2 approved with reservations]. NIHR Open Res 2026, 6:3 (https://doi.org/10.3310/nihropenres.14151.1) NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article. Export Citation Sciwheel EndNote Ref. Manager Bibtex ProCite Sente Select a format first ▬ ✚ Study Protocol [version 1; peer review: 2 approved with reservations] Sisay Abayneh https://orcid.org/0000-0003-4944-0384 1,2, Laura Asher3, Caroline Smartt4, [...] Victoria Mutiso5, Peter Badimak Yaro6, Eleni Misganaw7, Kimberly Kariuki https://orcid.org/0000-0002-6818-7348 8, Faith Mukami9, Cecilia Ashaley Fofo6, Tizaa Hannan Legend6, Hasset Chenu7, Ursula Read10, Rosie Mayston11, Ribka Birhanu12, Atalay Alem12, Charlotte Hanlon https://orcid.org/0000-0002-7937-3226 1,13Sisay Abayneh https://orcid.org/0000-0003-4944-0384 1,2, Laura Asher3, [...] Caroline Smartt4, Victoria Mutiso5, Peter Badimak Yaro6, Eleni Misganaw7, Kimberly Kariuki https://orcid.org/0000-0002-6818-7348 8, Faith Mukami9, Cecilia Ashaley Fofo6, Tizaa Hannan Legend6, Hasset Chenu7, Ursula Read10, Rosie Mayston11, Ribka Birhanu12, Atalay Alem12, Charlotte Hanlon https://orcid.org/0000-0002-7937-3226 1,13 PUBLISHED 07 Jan 2026 Author details Author details 1 Centre for Innovative Drug Development and Therapeutic Trials for Africa (CDT-Africa), Addis Ababa University College of Health Sciences, Addis Ababa, Addis Ababa, Ethiopia 2 College of Education and Behavoural Sciences, Arsi University, Assela, Oromia, Ethiopia 3 Nottingham Centre for Public Health and Epidemiology, School of Medicine,, Institute of Mental Health, University of Nottingham, Nottingham, UK 4 Division of Psychiatry, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK 5 Africa Institute of Mental and Brain Health, Nairobi, Kenya 6 Basicneeds-Ghana, Accra, Ghana 7 Mental Health Service Users Association – Ethiopia, Addis Ababa,, Ethiopia 8 Kenya Medical Research Institute, Centre for Clinical Research, Division of Mental Health, Nairobi, Kenya 9 Mental 360 Kenya, Nairobi, Kenya 10 School of Health and Social Care, University of Essex, Colchester, UK 11 Department of Global Health and Social Medicine, King’s College London, London, UK 12 College of Health Sciences, School of Medicine, Department of Psychiatry and WHO Collaborating Centre in Mental Health Research and Capacity-Building, Addis Ababa University, Addis Ababa, Ethiopia 13 Division of Psychiatry, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK 2 College of Education and Behavoural Sciences, Arsi University, Assela, Oromia, Ethiopia 3 Nottingham Centre for Public Health and Epidemiology, School of Medicine,, Institute of Mental Health, University of Nottingham, Nottingham, UK 4 Division of Psychiatry, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK 5 Africa Institute of Mental and Brain Health, Nairobi, Kenya 6 Basicneeds-Ghana, Accra, Ghana 7 Mental Health Service Users Association – Ethiopia, Addis Ababa,, Ethiopia 8 Kenya Medical Research Institute, Centre for Clinical Research, Division of Mental Health, Nairobi, Kenya 9 Mental 360 Kenya, Nairobi, Kenya 10 School of Health and Social Care, University of Essex, Colchester, UK 11 Department of Global Health and Social Medicine, King’s College London, London, UK 12 College of Health Sciences, School of Medicine, Department of Psychiatry and WHO Collaborating Centre in Mental Health Research and Capacity-Building, Addis Ababa University, Addis Ababa, Ethiopia 13 Division of Psychiatry, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK Sisay Abayneh Roles: Conceptualization, Methodology, Project Administration, Writing – Original Draft Preparation, Writing – Review & Editing Roles: Conceptualization, Methodology, Project Administration, Writing – Original Draft Preparation, Writing – Review & Editing Laura Asher Roles: Methodology, Writing – Review & Editing Roles: Methodology, Writing – Review & Editing Caroline Smartt Roles: Writing – Review & Editing Roles: Writing – Review & Editing Victoria Mutiso Roles: Writing – Review & Editing Roles: Writing – Review & Editing Peter Badimak Yaro Roles: Writing – Review & Editing Roles: Writing – Review & Editing Eleni Misganaw Roles: Writing – Review & Editing Roles: Writing – Review & Editing Kimberly Kariuki Roles: Writing – Review & Editing Roles: Writing – Review & Editing Faith Mukami Roles: Writing – Review & Editing Roles: Writing – Review & Editing Cecilia Ashaley Fofo Roles: Writing – Review & Editing Roles: Writing – Review & Editing Tizaa Hannan Legend Roles: Writing – Review & Editing Roles: Writing – Review & Editing Hasset Chenu Roles: Writing – Review & Editing Roles: Writing – Review & Editing Ursula Read Roles: Writing – Review & Editing Roles: Writing – Review & Editing Rosie Mayston Roles: Writing – Review & Editing Roles: Writing – Review & Editing Ribka Birhanu Roles: Writing – Review & Editing Roles: Writing – Review & Editing Atalay Alem Roles: Funding Acquisition, Writing – Review & Editing Roles: Funding Acquisition, Writing – Review & Editing Charlotte Hanlon Roles: Conceptualization, Funding Acquisition, Methodology, Writing – Review & Editing Roles: Conceptualization, Funding Acquisition, Methodology, Writing – Review & Editing OPEN PEER REVIEW REVIEWER STATUS 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. 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. 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 People experiencing both homelessness and severe mental illness (a group of illnesses such as schizophrenia that greatly interfere with life activities) have many unmet needs. Fulfilling these needs requires coordinated involvement of many organizations and individuals. There is a lack of evidence, particularly in developing countries, regarding the interventions available to address these complex needs. This protocol details how we will synthesize evidence and develop a programme theory to explore what interventions might work to address the unmet needs of people who are homeless and have severe mental illness, for whom, and under what circumstances and why interventions these interventions work, We will work with key stakeholders including people who are homeless and have severe mental illness throughout the study process. The findings will inform the development of contextually relevant programme theories to address the unmet needs of this population in developing countries. Homelessness; programme theory; realist approach; severe mental illness Corresponding Author(s) Sisay Abayneh ([email protected]) Grant information: This project is funded by the National Institute for Health and Social Care Research (NIHR) through the Global Health Research Group on Homelessness and Mental Health in Africa (Grant Reference Number NIHR134325). The views expressed in this publication are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care or Public Health England. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Copyright: © Crown copyright, 2026 Abayneh S et al.. This open access work is licensed under the Open Government Licence v3.0 How to cite: Abayneh S, Asher L, Smartt C et al. Developing programme theories to address unmet needs of people experiencing homelessness and severe mental illness: protocol for a realist review [version 1; peer review: 2 approved with reservations]. NIHR Open Res 2026, 6:3 (https://doi.org/10.3310/nihropenres.14151.1) First published: 07 Jan 2026, 6:3 (https://doi.org/10.3310/nihropenres.14151.1) Latest published: 07 Jan 2026, 6:3 (https://doi.org/10.3310/nihropenres.14151.1) The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Homelessness is an increasing global public health and human rights crisis1. It is estimated that 150 million people worldwide are homeless2, and approximately 1.8 billion people lack adequate housing3. This is likely underestimated because of variations in how homelessness is defined between contexts and due to the lack of data. There is heterogeneity in the homeless population over time and across societies4. Generally, homelessness refers to a broad range of housing exclusion and precarity that ranges from living in unsuitable or inadequate housing to sleeping on the streets5,6. Evidence, mainly from the Global North, has shown that people who are homeless experience a wide range of health inequalities including disproportionately higher all-cause mortality7, discrimination and stigma8, and higher risk of ill-health mental9–11 compared to the general population. Co-occurrence of homelessness and mental health conditions has substantial negative consequences, including an increased risk of suicide and substance abuse, poorer physical health and wellbeing, increased personal and structural barriers to accessing and utilizing services, challenges in finding secure accommodation, and reduced life expectancy7,9. People who are homeless and have a severe mental illness (SMI), e.g., schizophrenia, bipolar disorder, and major depressive disorder12 are at especially increased risk of unemployment, and poor retention in employment, severe poverty, lack of social support, stigma and discrimination1,8,13, lack of access to healthcare14,15, worse quality of life, and complex unmet needs16. There are systematic reviews of several interventions for people who are homeless and have SMI, including critical time intervention17, “case management” interventions that involve collaborative process where people with a lived experiences of health condition assigned professionals who assess, plan, facilitate, monitor and advocate for option to meet their needs18,19, housing support and income assistance20,21, “assertive community treatment”, i.e. specialized long-term community-based individualized, holistic models of treatment and support services delivered by multi-disciplinary team22, peer support, and life skills training23. These reviews suggested a range of positive impacts e.g., reducing homelessness, reducing hospitalizations, and improving quality of life. However, these systematic reviews have largely involved studies conducted in high-income countries, with no meaningful suggestions on how to address the varied needs of people who are homeless in diverse low-and middle-income countries (LMICs). Furthermore, systematic reviews provide little consideration of the contextual complexities, and non-linear causal interactions between interventions, contexts, actors, mechanisms, and outcomes in complex social interventions24–27. However, to the best of our knowledge, few existing reviews have used theory-driven (e.g., realist) approaches to account for the complexity of interventions for people who are homeless and have SMI, and how to implement such interventions in particular contexts that may differ in important ways25–27. The proposed review, therefore, aims to fill this gap through a realist synthesis of evidence to inform the development of a contextualized and transferable programme theory of interventions to address the needs of people who are homeless with SMI in LMICs. Realist review, or realist synthesis, is an interpretative, theory-driven, explanatory approach to evidence synthesis that investigates how a particularly complex intervention or programme functions in complex environments28,29. Realist theory enables contextualization and transferability of findings across settings through unearthing the underlying causal mechanism and construction of abstract mid-range theories by augmenting with formal theories (See Table 1 for definitions of key realist concepts)30,31. The proposed review is being conducted to inform a wider study nested within the National Institute for Health and Care Research (NIHR) Global Health Research Group on Homelessness and Mental Health in Africa (HOPE) in Ethiopia, Ghana, and Kenya. In HOPE, we will use participatory methods to develop and evaluate community-based interventions to address the unmet needs of people who are homeless and have SMI living in LMICs in ways that are rights-based, contextually grounded, scalable, and sustainable32. The current study will occur in three phases: development of initial programme theories (IPTs) through the proposed realist review outlined in this protocol (Phase1); testing and refining the IPTs (Phase2); and generating middle-range theory (Phase3). | Intervention(I): a combination of policy or programme components, implemented activities, strategies, and resources to bring change37. | | Context(C): elements in the background environment of the intervention that may have an impact on outcomes, including individual characteristics and capacities (demographic factors, knowledge, attitudes, health status, motivation, etc), interpersonal relationships between stakeholders, institutional/organizational factors (structures, policies, rules, norms and culture of the organization), and the wider social, economic, political, geographic, cultural conditions and policy infrastructures external to the interventions that trigger the mechanism, which then determine the programme outcomes28,29,38. | | Actors(A): individuals, groups, and institutions who are addressed by the intervention, and who play key roles in the implementation and uptake of an intervention37. | | Mechanisms (M): underlying causal or hidden generative forces that lead to outcomes, which often denote resources, reasoning, and decisions that actors make due to the resources provided by the programme. Mechanisms are not interventions or strategies themselves (e.g. training courses), but rather the response (e.g. why training changes behavior or does not) that is created as a result of the strategy or resource37. | | Outcomes(O): short-, medium- and long-term changes (both intended and unintended) resulting from mechanisms activated within specific contexts when actors received interventions37. | | Formal/substantive theory: existing theories that have been well-established within certain disciplines that help identify mechanisms or features of context and explain how overall sets of findings fit together39. | | Programme theory: a set of explicit or implicit assumptions summarising how the programme is organized and works40. | | Mid-range theories: more abstract and generalizable than ‘programme theories’ but do not constitute a ‘grand social theory’ themselves; instead, they are considered adaptive and cumulative explanations40. | | Abductive thinking: an interactive process of examining evidence and developing hunches or ideas about the causal factors linked to that evidence, for example, potential mechanisms to be investigated, based on what feels right, logic, what ideas surface based on data or clues40. | | Retroductive thinking: a form of inference that aims to uncover the underlying (hidden) causal mechanisms or structures that give rise to observed phenomena. This process requires the use of common sense, expertise, and imagination to build and test theories about underlying causal processes40. | | Demi-regularities: the idea that there are patterns in the world that tend to occur under certain conditions or contexts, but these regularities are not fixed and invariant and are sensitive to contextual factors40. | The general objective of the proposed review is to conduct a realist synthesis of theoretical and empirical evidence, combined with formative work completed as part of the HOPE project, and to develop a programme theory explaining what interventions work, how, why, for whom, and in what circumstances to address the unmet needs of people who are homeless and have SMI in Ethiopia, Ghana, and Kenya. The specific objectives are to: Identify outcomes linked to interventions; Explore mechanisms through which community-based interventions address unmet needs; Identify key contextual individual, organization, community, and structural influences likely to determine whether the mechanisms produce the intended outcomes; and Describe the causal links between the intervention, context actors, and mechanisms, leading to improved outcomes for people who are homeless and have SMI. Patient and Public Involvement, defined as research being carried out ‘with’ or ‘by’ members of the public, rather than ‘to’, ‘about’ or ‘for’ them33, is a key feature of realist approaches. Extensive and interactive engagement with relevant stakeholders helps to ensure authentic, contextually relevant evidence, clarity, and the transferability of findings34–36. The HOPE project, in which the current research protocol was nested, has been working with a multi-stakeholder partnership of researchers, policy makers, practitioners, and people with lived experience of mental illness (Lived Experience Advisory Group-LEAG) starting from the HOPE project proposal development. Each HOPE country team (Ethiopia, Kenya, and Ghana) established a multi-sectoral Community Advisory Board (CAB) that meets at key stages to guide and inform the project32. Similarly, during the development of this realist review protocol, key stakeholders including multidisciplinary professionals and people with lived experiences of mental illness (n=7) involved throughout the protocol development process and included as co-authors. We will draw on patient and public involvement as part of our active stakeholder engagement throughout the actual study phases. Accordingly, we will convene a separate Research Advisory Group (RAG). The RAG members will comprise multidisciplinary professionals and researchers with combined relevant expertise in the area of people who are homeless and have SMI, complex intervention design, and people with experiential knowledge of homelessness and SMI. The members will be selected from the HOPE multi-stakeholder consortium members, including investigators from each HOPE project country, all members of the LEAG, and other relevant professionals. The RAG will provide methodological guidance and feedback throughout the study phases. In addition to the RAG, we will actively involve and work with the LEAG throughout the review process. The LEAG and RAG will meet online at least three times (along with continuous e-mail exchanges) during the review process. Key findings of each phase of the review will be presented, and feedback will be obtained from the LEAG and RAG. Notes of the meetings will be kept on programme theory to maintain an audit trail of the decisions made and improvement of the findings. Homelessness is often described as a “wicked problem”, which refers to a complex problem resulting from multilevel and interacting individual, interpersonal, organizational, and systemic factors, which require a coordinated solution from many stakeholders, including social and political actors41–43. Co-occurrence of homelessness and SMI requires approaches for evidence synthesis and intervention development which are able to account for complexity1,26,44. Theory-driven approaches such as realist review is appropriate for a deeper understanding of complex social programmes within heterogeneous social contexts26,35,45. Unlike traditional systematic reviews that focus on whether interventions work, realist reviews focus not only on “what works” or the effectiveness evaluation of interventions but also on the underlying theories and mechanisms. This offers an opportunity for generating context-sensitive causal explanations about how, why, for whom, and in what contexts interventions work or do not work24,29. Realist reviews bring together evidence and insights from multiple sources, allowing synthesis and triangulation of theoretical and empirical evidence. This approach promotes stakeholder engagement, optimizes learning and generates accessible recommendations for policy and practice that can be applied in different settings28,40,46. Furthermore, realist reviews aim to recognize and account for the complexity and non-linear causal relationships of social systems at multiple levels: macro-level (systemic external situations that influence the function of the programme), meso-level (organizational culture, rules, regulations, structure and functioning of services), and micro-level (knowledge, attitudes, skills, values, health, and behaviour of individuals involved in the programme)29,40,47. In realist approaches, the social world is understood by identifying underlying causal mechanisms using generative causation through realist logic. Realist logic includes inductive, deductive, abductive, and retroduction reasoning (See Table 1 for definitions of key realist concepts)48–50. As a theory-driven approach, realist review begins with IPTs and ends with a refined programme theory that explains how a complex intervention or programme works29,34,40. Programme theories are typically expressed as context-mechanism-outcome (CMOs) configurations29,38,51. For the proposed review, we will use the expanded model of intervention-context-actors-mechanisms-outcome configurations (ICAMOs)37,49,52. The ICAMO approach postulates that “outcome(O) is produced by mechanism(M) activated in context(C) through actors(A) when interventions(I) are implemented”53. Realist approaches recognize that interventions and actors interact within their social reality, which also influences how the intervention is implemented and how the actors respond (or not) to the resources offered by the intervention39,54. The ICAMO configurations make programme resources more explicit (i.e. differentiate intervention from context), and seek to clarify actors' roles, perspectives, and reasoning in designing and implementing interventions37,49. There are several ways to conduct a realist review, each with a different number of iterative steps35,55. This review will be informed by the iterative stages set out by Pawson et al.29,56, and recent realist review methodological papers that provide further depth and information regarding searches, data extraction, analysis, and synthesis approaches48,55,57,58. The findings will be reported according to established realist quality and publication standards: Realist and Meta-narrative evidence syntheses–Evolving standards (RAMESES)24,59. Each stage will incorporate stakeholder consultations. The review protocol for this study was preregistered with the International Prospective Register of Systematic Reviews (PROSPERO, CRD420251067136); and the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocols (PRISMA-P)60 checklist can be found online on Open Science Framework, https://doi.org/10.17605/OSF.IO/G432U61. The stages of the review are illustrated in Figure 1, and detailed below. 1. Step 1. Clarifying the scope of the review Different approaches can be used to clarify the scope of the study and identify/develop IPTs; for example, informal scoping reviews, programme documents, systematic reviews of scholarly articles, and interviews or focus groups with stakeholder groups62. In this study, we will use multiple data sources. We will conduct a preliminary informal literature search to identify existing literature about interventions for people who are homeless and have SMI. More importantly, we will synthesise findings from formative work conducted in the HOPE project32. This includes a systematic review63, a global expert consultation exercise, and ethnographies, surveys, theory of change workshops and intervention mapping within the study sites in Ethiopia, Ghana and Kenya. The HOPE systematic review aims to identify interventions for people who are homeless and have SMI in LMICs, as described elsewhere32. Findings will provide information on the scope of existing evidence, types of interventions, and implementation strategies in LMICs, which can inform the scope of the proposed review. In our study, we will deductively analyse data from the formative works and scoping review to identify the intervention, context, actors, mechanisms and outcomes (ICAMO). We will create a codebook for the elements of ICAMO. The codebook will guide the deductive coding of relevant documents and serve as starting point for stakeholder consultations and the literature review58,64. The ICAMO configurations will then be mapped using the realist logic of abductive and retroductive theorizing to develop the IPTs50. The IPTs will be formulated as early working hypotheses structured in the format “if…then…because” statements, which make tentative links between ICAMO elements and explanations of which interventions address the unmet needs of people who are homeless and have SMI, for whom, how, why and in which contexts59,65. We will conduct a scoping review of literature to locate existing formal theories (also called substantive theories) to provide a framework to inform the development of the IPTs39. Formal theories are pre-existing theories within a range of disciplines, such as behavioural sciences, social sciences, at a higher level of abstraction than programme theories, which provide a bridge to a wealth of existing research and knowledge about a topic39,49,66. Formal theories help interrogate IPTs about how an intervention brings about change at multiple levels (individual, interpersonal, institutional, infrastructural, and structural)24,39,67. We will conduct a scoping review using the BeHEMoTh approach (behaviour of interest, health context, exclusions, models or theories) to locate existing formal theories in studies for people who are homeless and SMI68. The identified formal theories will be presented for stakeholder groups (described below) to select and prioritize relevant theories which inform IPT development. 2. Search for evidence Relevant academic literature will be used to refine the IPTs and test the hypotheses formulated in Stage 124,58. The process of searching, screening and analyzing relevant material in a realist review is not a single-point exercise and has no one prescribed method. Rather, the process requires ongoing multiple iterations, and different search methods to support the different components of the realist synthesis process (See Figure 1)24,55,58. In the proposed review, formal and additional searches will be conducted. Details of the search process and record of any subsequent alterations will be documented in a research logbook to provide transparency and enhance the quality of the review24,55. A formal search for published documents will be conducted in databases, which include MEDLINE, PsycINFO, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL), Global Health, Cumulative Index to Nursing and Allied Health Literature (CINAHL), PsycARTICLES, Web of Science, Global Index Medicus; Applied Social Sciences Index and Abstracts (ASSIA), and International Bibliography of the Social Sciences (IBSS). Many of these sources are chosen due to their use in the HOPE systematic review related to this study69. The search terms will be adapted from the HOPE systematic review, but increasing the scope by not restricting the search to LMICs. Where necessary, we will use complimentary search techniques such as ‘CLUSTER’ searching (Citations; Lead author; Unpublished materials; Scholar searches; Theories; Early examples; Related projects), to identify associated additional documents that might add to the conceptual and contextual richness of documents identified in the formal search70. This search will be purposive, directed by emerging programme theories using search techniques such as searching for "sibling" (i.e., directly linked outputs from a single document) or "kinship" (i.e., associated papers with a shared contextual or conceptual pedigree) papers associated with included documents55,70,71. We will also conduct forward and backward citation searches, using Google Scholar to identify further related papers from the wider literature. Searching will continue until sufficient data are found (‘theoretical saturation’) to conclude that the refined programme theories are sufficiently coherent and plausible24,55. We will apply pre-determined inclusion and exclusion criteria, which will likely be refined in light of the emerging data and theoretical development as the review progresses24. The eligibility criteria will be broad and include the following: Study designs: In keeping with RAMESES guidelines24,59, there are no restrictions on the types of study designs. However, given that there is a large body of systematic reviews available on various intervention types for people who are homeless and have SMI, to limit the scope of our review and be pragmatic due to time constraints, a systematic review of reviews (quantitative as well as qualitative) will be considered. Population: The population of interest for this review is adults aged 16 years or above who are homeless and have SMI. Homelessness is operationalised as “(a) literal (street) homelessness, (b) residence in a homeless shelter, squatting, (c) admission in a psychiatric facility, jail or religious healing facility with no place of residence to go post-discharge, and (d) previous street homelessness. This definition excludes the following groups: (a) individuals described as “unstably housed, which include people living in overcrowded homes, living in substandard places with inadequate amenities)”, (b) “landless” individuals, or those living in accommodation with insecure tenancy, (c) individuals living in slum/shantytowns but in stable accommodation, (d) internally displaced people, (e) child homeless populations”16. SMI will be operationalised as “diagnosis of schizophrenia, schizoaffective disorder, bipolar disorder with psychotic features, and major depression with psychotic features according to ICD-10/DSM-V guidelines or clinical assessment. We will also include studies that use the broader terms of SMI, psychosis, psychosocial disability, mental disability, people who are homeless with comorbid SMI and alcohol/substance use disorders”16. We will exclude people with substance use disorders without SMI; people with SMI who are at risk of homelessness, and people living in substandard housing. Intervention(s): The main interventions identified from the HOPE intervention mapping exercise and co-produced ToC include, but are not limited to, are community-based interventions intended to address the multifaceted complex unmet needs of people who are homeless and have SMI. These include: housing interventions (including supported living, community-based residential interventions), self-help, peer support, drop-in centres (e.g., day centres), empowerment interventions (i.e. interventions to strengthen exercise of human rights and/or to increase involvement of people who are homeless and have SMI in their own care and/or service improvement and/or system strengthening), recovery or rehabilitation (e.g., community-based rehabilitation), family-based interventions, substance use interventions, physical health interventions, non-governmental organization-based interventions, livelihood/vocational interventions (i.e. any interventions to improve economic status or livelihoods at the individual and/or family level), interventions to increase engagement in education, interventions designed to increase social inclusion of people with lived experience of homelessness and SMI, psychological interventions, other support interventions (such as provision of food/clothing/other basic needs), service models for delivery of care, and studies to support medication adherence or to safely manage discontinuation. However, we will exclude efficacy studies of pharmacological interventions, and studies of long-term institutionalization. Contexts: We are looking for evidence about interventions in largely community-based settings (excluding humanitarian settings) for people who are homeless and have SMI. Intervention settings may include residential settings (including temporary or long-term shelters/hostels), the health system (primary, secondary and specialist mental health care levels), and traditional or religious facilities. The review will have no restriction by geography. We will thus extend the HOPE systematic review, which focused solely on LMICs. Outcomes: The outcomes of interest include, but are not limited to those prioritised by people who are homeless and have SMI as identified from the HOPE ethnographies and surveys in Ethiopia, Ghana and Kenya, and identified by the HOPE global expert consultation and systematic review. Domains of relevant outcomes include basic needs (water, food, self-care, clothing, shelter), social needs, clinical outcomes (mental and physical health, mortality), livelihood (economic outcomes at the individual and/or household levels), social inclusion, empowerment (i.e. strengthening of human rights, support or advocacy for people who are homeless and their caregivers), and quality of life/well-being. Language: English Publication dates: We will restrict our focus to studies published within the past 10 years (2015–2025) to ensure the findings reflect the relatively contemporary landscape of programmes for people who are homeless and have SMI. 3. Document selection and appraisal Screening All data sources will be exported to Endnote X7 reference manager. Selection will be accomplished in stages. First, author SA will screen all potentially relevant documents retrieved by title and abstract for relevance against inclusion and exclusion criteria detailed above. Second, the full-texts of documents deemed to meet the inclusion criteria will be read in detail and assessed for relevance, richness, and rigor as detailed below24,36,48. A random sample of 10% of documents at the two screening stages will be checked by another reviewer for consistency of application of screening criteria. Any disagreement will be resolved through discussion or if necessary, by consulting with the rest of the team. Appraisal of the studies will use the criteria of relevance, richness and rigour48. The relevance of a document refers to its ability to provide information related to theory building, testing, and the review`s aims and objectives24,35,48. Rigor in realist approaches refers to the credibility, plausibility, and trustworthiness of the methods used to generate the relevant data or a theory24,48. Assessment of rigor will focus on the extent to which a document/study provides a detailed description of their methods (e.g., sample size, data collection, data analysis), whether specific inferences drawn have sufficient support to make a methodologically substantial influence when developing/testing IPTs, and how reliable and generalizable their findings are based on those methods24,35,48. This traditional assessment of rigor should be balanced, as “nuggets of wisdom” for realist review can be found in methodologically weak studies according to the conventional hierarchy of evidence36,72. Hence, in line with realist review practices, we will not exclude any study based on rigor; rather, studies providing relevant evidence will be included, and results of appraisal of rigor will be included for transparency73. Richness refers to the level of theoretical and conceptual depth and detail provided in a document24,48,70. This help to assess the extent to which texts could provide in-depth explanation of how and why an intervention worked70. Sources can have ‘conceptual richness’ and/or ‘contextual thickness’70. Contextual thickness entails sufficient detail that enables the reader (i) to establish what is occurring in the intervention and the wider context and (ii) to infer whether findings can be transferred to other people, places, situations, or environments. Appraising for richness ensures only sources that can meaningfully contribute to the research question are included, making the review manageable and the findings more relevant48,74. For all studies that meet our eligibility criteria and are included in the review, data quality appraisal will be undertaken using predefined criteria for assessment of relevance, richness, and rigor adapted from published studies (See Table 2)75. Each article will be appraised and classified into high, medium and low ratings for each appraisal category depending on its contribution to IPT development and established methods used in previous studies35,48,75. No article will be excluded or included based on just one criterion, judgement will be made based on the overall value added to the research question. 4. Data extraction. SA will design and pilot a bespoke data extraction form in a Microsoft Excel spreadsheet to extract text segments across each full-text study deemed to be relevant, rich, and rigour congruent with realist review guidelines35,58. First, studies classified as high according to our appraisal will be extracted followed by those rated medium/moderate and finally low richness papers will be extracted for any additional data or insights that could contribute to the refinement of IPTs. Data extraction will stop when theoretical saturation is reached (until the literature no longer contributes novel insights)48. SA will independently complete the extraction of data. Information will be captured on each document a characteristic includes: author(s), publication year, methods/design, population/participant demographics, setting, and key findings. In addition, elements of ICAMO will be extracted separately for each included study using the coding framework. For quantitative studies, rather than extracting numerical data, description of key findings and author`s interpretation will be captured. A random 10% sub-sample of data extraction documents will be reviewed independently by one other reviewer for accuracy. Any disagreement between the reviewers will be recorded and resolved through discussion or in consultation with a third reviewer. 5. Data analysis and synthesis. Data analysis and synthesis are intended to find and align evidence using realist logic to make sense of the different data contributions and refine the IPTs29,36. For the proposed study, these will be informed by the processes outlined by realist methodological papers, which will involve formulating ICAMO configurations at multiple levels, consolidating recurring patterns or demi-regularities, and conceptual mapping/theory building35,57,76. First, we will conduct a deductive thematic analysis of extracted data from each article and categorize them into the ICAMO components using a coding framework developed based on the IPTs in Step 1. The extracted data will be organized into an evidence table of ICAMO elements. The ICAMOs will be linked to the earlier IPTs to iteratively refine them into programme theories (PTs) by testing them against the ICAMO using a retroductive approach to uncover the causal mechanisms behind observed outcomes50,77,78. Secondly, we will consolidate recurrent ICAMO configurations into demi-regularities (statements of what works, for whom, and in what circumstances)57,76,79. We will explore patterns within the ICAMO configurations and apply thematic labels based on similarity (categorizing conceptually similar ICAMOs)57,80,81. The consolidation process helps manage and reduce large amounts of data through grouping or categorizing conceptually similar IPTs57. Finally, we will use the process of configurational mapping to create a visualization of the findings framed within the ICAMO model to explain the programme theory37,57,79. We will use a conceptual map, such as feedback loop diagrams/causal loops, as an analytical strategy to map out pathways to identify and represent the elements of ICAMO and to illustrate the links between these constructs. This will help us to develop refined programme theories for people who are homeless and have SMI57,77. Realist scholars contend that interventions are influenced by various levels of contexts(individuals, interpersonal, institutional settings, infrastructures/structural)82. We will inform the refined IPTs with relevant formal theories that support theorizing at these multilevel contexts39,83 and construct conceptual maps depicting their relationships systemically57,76,79. This analysis will enable us to understand the most relevant and important mechanisms that work at different levels and build more transferrable IPTs across various settings77. The refined IPTs will be presented and discussed with the RAG and LEAG for further feedback and to ensure an appropriate interpretation of results, contextual sensitivity, rigor, trustworthiness, coherence, and plausibility of the refined IPTs24,65. The findings from this review, namely the refined programme theories, will be evaluated through realist evaluation of the intervention using a multiple case study design in Ethiopia, Ghana, and Kenya. The realist evaluation will enable further refinement of the programme theories through real-world testing. Then, the findings of the realist evaluation will be supported by relevant formal theories to substantiate the inferences made, make sense of the patterns of findings (demi-regularities) of emerging ICAMO configurations from HOPE pilot evaluation empirical studies, and develop middle-range theory (MRT), which will be transferable to wider contexts24,34,39,49. This greater clarity on ICAMOs can further enhance transferability of the HOPE programme across different settings and usefully inform efforts to meet the needs of people who are homeless and have SMI. This paper describes the protocol of a realist review that aims to explore what interventions work for people who are homeless and have SMI, for whom, in what circumstances, how, and why in diverse LMIC settings. The proposed review forms the first phase of a wider study intended to develop a theory-driven programme to address this population's unmet needs, which will be tested and evaluated through realist evaluation using multiple case studies in Ethiopia, Ghana, and Kenya. To our knowledge, this is the first realist review aiming to use theory-driven evidence synthesis of interventions and develop programme theory for people who are homeless and have SMI to be evaluated in LMICs. There are several systematic reviews of various interventions for people who are homeless and have SMI, mainly from the global North17,18,21–23. Nevertheless, these reviews have focused on what works, and little is known about underlying causal mechanisms, and how findings are applied in different contexts. There is little theory-driven evidence synthesized that takes into account the complexity of the interventions, mechanisms underlying effective interventions and in which contexts the desired outcomes are most likely to be achieved1,26. The conventional systematic review approach does not support transferability of findings to diverse contexts84. The realist methodological approach described in this protocol paper adds to existing knowledge, and complements it by developing programme theory that enables theoretical transferability and applicability of findings in different contexts35,38. Several strengths of the realist approach make it well-suited to consider developing programme theory for complex interventions for people who are homeless and have SMI35. The realist review will provide the opportunity for synthesizing different pieces of evidence and working with a diverse group of stakeholders, including people with lived experiences, which will enhance a range of perspectives, the rigor and transparency of the evidence, and will improve the practical utility of the findings and accessible outputs that meet local needs24,29. The diverse data sources and methodologies allow for examining interventions, contexts, actors, and mechanisms that lead to outcomes to develop programmes with wider context transferability38,85. Further, a realist review can produce important information about the relative effectiveness of intervention components, thereby enabling practitioners, researchers, and service providers to design and implement interventions comprising only effective components for particular contexts86. The proposed realist review will comply with evidence-based practices29,87, hence the findings will inform a further evaluation of programme theories in a realist evaluation. We systematically outline each step including IPT development, the search strategy, extraction and analysis procedures, including coding methods and evidence synthesis to ensure replicability35. CAB: Community-Advisory Board; CMO: Context-Mechanism-outcomes; ICAMO: Intervention-context-actor-mechanism-outcomes; IPT: Initial programmed theory, LEAG: Lived Experience Advisory Group; LMICs: Low and middle-income countries; NIHR: National Institute for Health and Care Research; RAG: Research Advisory Group, RAMESES: Realist and Meta-narrative evidence syntheses–Evolving standards Ethical approval is not needed for this protocol because this is a review and synthesis of literature in the public domain, and stakeholder groups will be involved to provide feedback and guidance based on their expertise and experience, but no data will be collected from them. No data are associated with this article Abayneh S, Asher, L., Smartt, C., Mutiso, V., Yaro, P. B., Misganaw, E., … Hanlon, C. Developing programme theories to address unmet needs of people experiencing homelessness and severe mental illness: protocol for a realist review. 2025. https://doi.org/10.17605/OSF.IO/G432U. This project contains the following underlying data: PRISMA-P checklist. Data are avaliable undert terms marked CC0 1.0 Universal Public Domain Dedication. CH and AA receive funding support from Wellcome through grant 222154/Z20/Z. CH also receives support from Wellcome grant 223615/Z/21/Z. AA also receives funding from Developing Excellence in Leadership, Training and Science Initiative II (DELTAS Africa II) Grant a joint funding support from Wellcome Trust and UK’s Foreign, Commonwealth and Development Office (FCDO). Faculty Opinions recommendedReferences - 1. Fowler PJ, Hovmand PS, Marcal KE, et al.: Solving homelessness from a complex systems perspective: Insights for prevention responses. Annu Rev Public Health. 2019; 40: 465–486. PubMed Abstract | Publisher Full Text | Free Full Text - 2. 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PubMed Abstract | Publisher Full Text Author details Author details 1 Centre for Innovative Drug Development and Therapeutic Trials for Africa (CDT-Africa), Addis Ababa University College of Health Sciences, Addis Ababa, Addis Ababa, Ethiopia 2 College of Education and Behavoural Sciences, Arsi University, Assela, Oromia, Ethiopia 3 Nottingham Centre for Public Health and Epidemiology, School of Medicine,, Institute of Mental Health, University of Nottingham, Nottingham, UK 4 Division of Psychiatry, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK 5 Africa Institute of Mental and Brain Health, Nairobi, Kenya 6 Basicneeds-Ghana, Accra, Ghana 7 Mental Health Service Users Association – Ethiopia, Addis Ababa,, Ethiopia 8 Kenya Medical Research Institute, Centre for Clinical Research, Division of Mental Health, Nairobi, Kenya 9 Mental 360 Kenya, Nairobi, Kenya 10 School of Health and Social Care, University of Essex, Colchester, UK 11 Department of Global Health and Social Medicine, King’s College London, London, UK 12 College of Health Sciences, School of Medicine, Department of Psychiatry and WHO Collaborating Centre in Mental Health Research and Capacity-Building, Addis Ababa University, Addis Ababa, Ethiopia 13 Division of Psychiatry, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK 2 College of Education and Behavoural Sciences, Arsi University, Assela, Oromia, Ethiopia 3 Nottingham Centre for Public Health and Epidemiology, School of Medicine,, Institute of Mental Health, University of Nottingham, Nottingham, UK 4 Division of Psychiatry, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK 5 Africa Institute of Mental and Brain Health, Nairobi, Kenya 6 Basicneeds-Ghana, Accra, Ghana 7 Mental Health Service Users Association – Ethiopia, Addis Ababa,, Ethiopia 8 Kenya Medical Research Institute, Centre for Clinical Research, Division of Mental Health, Nairobi, Kenya 9 Mental 360 Kenya, Nairobi, Kenya 10 School of Health and Social Care, University of Essex, Colchester, UK 11 Department of Global Health and Social Medicine, King’s College London, London, UK 12 College of Health Sciences, School of Medicine, Department of Psychiatry and WHO Collaborating Centre in Mental Health Research and Capacity-Building, Addis Ababa University, Addis Ababa, Ethiopia 13 Division of Psychiatry, Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK Sisay Abayneh Roles: Conceptualization, Methodology, Project Administration, Writing – Original Draft Preparation, Writing – Review & Editing Roles: Conceptualization, Methodology, Project Administration, Writing – Original Draft Preparation, Writing – Review & Editing Laura Asher Roles: Methodology, Writing – Review & Editing Roles: Methodology, Writing – Review & Editing Caroline Smartt Roles: Writing – Review & Editing Roles: Writing – Review & Editing Victoria Mutiso Roles: Writing – Review & Editing Roles: Writing – Review & Editing Peter Badimak Yaro Roles: Writing – Review & Editing Roles: Writing – Review & Editing Eleni Misganaw Roles: Writing – Review & Editing Roles: Writing – Review & Editing Kimberly Kariuki Roles: Writing – Review & Editing Roles: Writing – Review & Editing Faith Mukami Roles: Writing – Review & Editing Roles: Writing – Review & Editing Cecilia Ashaley Fofo Roles: Writing – Review & Editing Roles: Writing – Review & Editing Tizaa Hannan Legend Roles: Writing – Review & Editing Roles: Writing – Review & Editing Hasset Chenu Roles: Writing – Review & Editing Roles: Writing – Review & Editing Ursula Read Roles: Writing – Review & Editing Roles: Writing – Review & Editing Rosie Mayston Roles: Writing – Review & Editing Roles: Writing – Review & Editing Ribka Birhanu Roles: Writing – Review & Editing Roles: Writing – Review & Editing Atalay Alem Roles: Funding Acquisition, Writing – Review & Editing Roles: Funding Acquisition, Writing – Review & Editing Charlotte Hanlon Roles: Conceptualization, Funding Acquisition, Methodology, Writing – Review & Editing Roles: Conceptualization, Funding Acquisition, Methodology, Writing – Review & Editing Competing interests No competing interests were disclosed. Grant information This project is funded by the National Institute for Health and Social Care Research (NIHR) through the Global Health Research Group on Homelessness and Mental Health in Africa (Grant Reference Number NIHR134325). The views expressed in this publication are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care or Public Health England. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Copyright © Crown copyright, 2026 Abayneh S et al.. This open access work is licensed under the Open Government Licence v3.0 metrics VIEWS $counts.viewCount downloads Citations CITE how to cite this article Abayneh S, Asher L, Smartt C et al. Developing programme theories to address unmet needs of people experiencing homelessness and severe mental illness: protocol for a realist review [version 1; peer review: 2 approved with reservations]. NIHR Open Res 2026, 6:3 (https://doi.org/10.3310/nihropenres.14151.1) NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article. track receive updates on this article Track an article to receive email alerts on any updates to this article. Current Reviewer Status: ? Key to Reviewer Statuses VIEW HIDE ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit. Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions Version 1 VERSION 1 PUBLISHED 07 Jan 2026 Views 0 How to cite this report: Wong G. Reviewer Report For: Developing programme theories to address unmet needs of people experiencing homelessness and severe mental illness: protocol for a realist review [version 1; peer review: 2 approved with reservations]. NIHR Open Res 2026, 6:3 (https://doi.org/10.3310/nihropenres.15398.r40162) The direct URL for this report is: https://openresearch.nihr.ac.uk/articles/6-3/v1#referee-response-40162 https://openresearch.nihr.ac.uk/articles/6-3/v1#referee-response-40162 NOTE: it is important to ensure the information in square brackets after the title is included in this citation. Reviewer Report 06 Apr 2026 Approved with Reservations VIEWS 0 I am not a content expert and so have restricted my comments to the area that I know something about, namely realist review/synthesis methodology. The protocol is clearly written and well referenced. The topic under consideration ... Continue reading I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above. Close The protocol is clearly written and well referenced. The topic under consideration ... Continue reading I am not a content expert and so have restricted my comments to the area that I know something about, namely realist review/synthesis methodology. The protocol is clearly written and well referenced. The topic under consideration - interventions to address the unmet needs of homeless and SMI people is correctly conceptualised as complex interventions and hence the use of a realist review approach is entirely suitable. The steps of the review are clearly articulated and reasonable. I have a few comments to make, the first being more important than the others. Firstly, relates to your initial programme theory development and then analysis in Step 5. Initially it may not be that helpful to try to develop detailed ICAMOs as part of your programme theory. Given that you may not have that much data at this stage, this 'absence' of data may mean that you may end up endlessly speculating about what is functioning as context or mechanism for each outcome of interest. Given your interest is to explain what 'works', for whom, when, why, how and to what extent for these interventions, perhaps a better use of your time might be to develop an initial programme theory that focusses on surfacing the underlying assumptions that underpin each intervention. In other words, why do the architects of the interventions think their intervention will work. Given that there may be quite a few intervention types or forms, you might find that it is more fruitful to group interventions not by type / form, but more by functions, and surface the assumptions behind each function. An example might be that there are various interventions that are outreach services - the assumption here is that people are more likely to engage with services when access is more convenient. However, I am no content expert, so do feel free to ignore if this is not going to be feasible. These assumptions then become the 'framework' for you to frame your analysis of the emerging data from your searches. It is then for these assumptions (and any more that you may identify from included documents) that you would then produce ICAMOs for. In other words, you are allocating more time to Stage 5, vs. Stage 1. Secondly, I have a number of minor comments: - you mention that you want to produce middle-range theory as one of your outputs of the review. I wondered if you mean middle-range programme theory? This is because middle-range theory is an adjective that describes the level of abstraction of a theory. See: Reference no. 1 - given you have existing reviews to draw on, you may want to explore if backwards and forwards citation tracking from the reference lists of these reviews may be a more efficient and quicker way to get to the documents you need. - you may want to specifically search for realist reviews / syntheses that are about access to services for different populations. This is because these may contain CMOCs that are relevant (but might need refining), since one property of mechanisms is that they are inherent liabilities of things or people. - it would be worth you provide a research question that your review seeks to answer. Good luck with your review. The protocol is clearly written and well referenced. The topic under consideration - interventions to address the unmet needs of homeless and SMI people is correctly conceptualised as complex interventions and hence the use of a realist review approach is entirely suitable. The steps of the review are clearly articulated and reasonable. I have a few comments to make, the first being more important than the others. Firstly, relates to your initial programme theory development and then analysis in Step 5. Initially it may not be that helpful to try to develop detailed ICAMOs as part of your programme theory. Given that you may not have that much data at this stage, this 'absence' of data may mean that you may end up endlessly speculating about what is functioning as context or mechanism for each outcome of interest. Given your interest is to explain what 'works', for whom, when, why, how and to what extent for these interventions, perhaps a better use of your time might be to develop an initial programme theory that focusses on surfacing the underlying assumptions that underpin each intervention. In other words, why do the architects of the interventions think their intervention will work. Given that there may be quite a few intervention types or forms, you might find that it is more fruitful to group interventions not by type / form, but more by functions, and surface the assumptions behind each function. An example might be that there are various interventions that are outreach services - the assumption here is that people are more likely to engage with services when access is more convenient. However, I am no content expert, so do feel free to ignore if this is not going to be feasible. These assumptions then become the 'framework' for you to frame your analysis of the emerging data from your searches. It is then for these assumptions (and any more that you may identify from included documents) that you would then produce ICAMOs for. In other words, you are allocating more time to Stage 5, vs. Stage 1. Secondly, I have a number of minor comments: - you mention that you want to produce middle-range theory as one of your outputs of the review. I wondered if you mean middle-range programme theory? This is because middle-range theory is an adjective that describes the level of abstraction of a theory. See: Reference no. 1 - given you have existing reviews to draw on, you may want to explore if backwards and forwards citation tracking from the reference lists of these reviews may be a more efficient and quicker way to get to the documents you need. - you may want to specifically search for realist reviews / syntheses that are about access to services for different populations. This is because these may contain CMOCs that are relevant (but might need refining), since one property of mechanisms is that they are inherent liabilities of things or people. - it would be worth you provide a research question that your review seeks to answer. Good luck with your review. - Is the rationale for, and objectives of, the study clearly described? Yes - Is the study design appropriate for the research question? Yes - Are sufficient details of the methods provided to allow replication by others? Yes - Are the datasets clearly presented in a useable and accessible format? Not applicable

1. RAMESES II Project: Theory in realist evaluation. https://www.ramesesproject.org/media/RAMESES_II_Theory_in_realist_evaluation.pdf. —.Competing Interests: No competing interests were disclosed. Reviewer Expertise: Realist review methodologist. CITE HOW TO CITE THIS REPORT Wong G. Reviewer Report For: Developing programme theories to address unmet needs of people experiencing homelessness and severe mental illness: protocol for a realist review [version 1; peer review: 2 approved with reservations]. NIHR Open Res 2026, 6:3 (https://doi.org/10.3310/nihropenres.15398.r40162) The direct URL for this report is: https://openresearch.nihr.ac.uk/articles/6-3/v1#referee-response-40162 https://openresearch.nihr.ac.uk/articles/6-3/v1#referee-response-40162 NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article. Views 0 How to cite this report: Handest R. Reviewer Report For: Developing programme theories to address unmet needs of people experiencing homelessness and severe mental illness: protocol for a realist review [version 1; peer review: 2 approved with reservations]. NIHR Open Res 2026, 6:3 (https://doi.org/10.3310/nihropenres.15398.r39162) The direct URL for this report is: https://openresearch.nihr.ac.uk/articles/6-3/v1#referee-response-39162 https://openresearch.nihr.ac.uk/articles/6-3/v1#referee-response-39162 NOTE: it is important to ensure the information in square brackets after the title is included in this citation. Reviewer Report 04 Feb 2026 Approved with Reservations VIEWS 0 This is a well-designed and timely protocol addressing a complex and important public health and social care challenge. The proposed realist review is a good methodological fit and a welcome contribution to a literature that is still dominated by effectiveness-oriented ... Continue reading I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard, however I have significant reservations, as outlined above. Close This is a well-designed and timely protocol addressing a complex and important public health and social care challenge. The proposed realist review is a good methodological fit and a welcome contribution to a literature that is still dominated by effectiveness-oriented reviews from high-income settings. The explicit focus on LMIC contexts in the Global South is particularly valuable. The integration within the HOPE programme, and the strong emphasis on stakeholder and lived experience involvement, are additional strengths. The protocol is generally clear and aligned with realist review guidance. I offer a few points where small clarifications would further strengthen transparency and robustness. First, the screening plan (10% double-screening at title/abstract and full-text stages) may leave some residual risk of inconsistent inclusion decisions—especially early in the review when IPTs are still evolving and relevance can be difficult to judge from abstracts. It would be helpful to justify the 10% threshold more explicitly and consider whether double-screening could be increased in early phases or in areas where disagreement is higher. Second, it is helpful that the protocol states all study designs are eligible and outlines theory-driven searching (e.g., CLUSTER, citation tracking, kinship/sibling papers). However, since a review of reviews “will be considered” for pragmatic reasons, it would strengthen the protocol to specify when reviews are expected to be sufficient for ICAMO development, and when primary studies (or linked cluster documents) will be purposively sampled to access mechanism- and context-rich data (e.g., actor reasoning and contextual contingencies). Third, the scope restrictions are reasonable but could be described more precisely. The protocol excludes pharmacological efficacy studies and long-term institutionalisation, while still covering a wide range of community-based interventions and service models (including supported living/residential community-based models). Given this nuance, consider adjusting the title so the intended scope is clearly signalled. Finally, unmet needs are clearly central to the aims, and the protocol usefully lists outcome domains (including those informed by lived experience and HOPE formative work). To avoid misinterpretation, it would help to state explicitly in the analytic plan that unmet needs (including persistence of unmet needs) will be treated as outcomes within ICAMO configurations, rather than being implicitly framed as residuals of intervention effectiveness. A short sentence on how evidence on intervention functioning will be used to explain both improvements and persistent unmet needs via specific context–mechanism interactions would strengthen the realist logic. Overall, this is a strong protocol. These targeted clarifications would further improve transparency and help maximise the explanatory value and transferability of the resulting programme theory. The protocol is generally clear and aligned with realist review guidance. I offer a few points where small clarifications would further strengthen transparency and robustness. First, the screening plan (10% double-screening at title/abstract and full-text stages) may leave some residual risk of inconsistent inclusion decisions—especially early in the review when IPTs are still evolving and relevance can be difficult to judge from abstracts. It would be helpful to justify the 10% threshold more explicitly and consider whether double-screening could be increased in early phases or in areas where disagreement is higher. Second, it is helpful that the protocol states all study designs are eligible and outlines theory-driven searching (e.g., CLUSTER, citation tracking, kinship/sibling papers). However, since a review of reviews “will be considered” for pragmatic reasons, it would strengthen the protocol to specify when reviews are expected to be sufficient for ICAMO development, and when primary studies (or linked cluster documents) will be purposively sampled to access mechanism- and context-rich data (e.g., actor reasoning and contextual contingencies). Third, the scope restrictions are reasonable but could be described more precisely. The protocol excludes pharmacological efficacy studies and long-term institutionalisation, while still covering a wide range of community-based interventions and service models (including supported living/residential community-based models). Given this nuance, consider adjusting the title so the intended scope is clearly signalled. Finally, unmet needs are clearly central to the aims, and the protocol usefully lists outcome domains (including those informed by lived experience and HOPE formative work). To avoid misinterpretation, it would help to state explicitly in the analytic plan that unmet needs (including persistence of unmet needs) will be treated as outcomes within ICAMO configurations, rather than being implicitly framed as residuals of intervention effectiveness. A short sentence on how evidence on intervention functioning will be used to explain both improvements and persistent unmet needs via specific context–mechanism interactions would strengthen the realist logic. Overall, this is a strong protocol. These targeted clarifications would further improve transparency and help maximise the explanatory value and transferability of the resulting programme theory. - Is the rationale for, and objectives of, the study clearly described? Yes - Is the study design appropriate for the research question? Yes - Are sufficient details of the methods provided to allow replication by others? Partly - Are the datasets clearly presented in a useable and accessible format? Yes Competing Interests: No competing interests were disclosed. Reviewer Expertise: My research focuses on psychopathology and social vulnerability in schizophrenia, as well as the role of classical psychopathological literature in modern clinical practice. CITE HOW TO CITE THIS REPORT Handest R. Reviewer Report For: Developing programme theories to address unmet needs of people experiencing homelessness and severe mental illness: protocol for a realist review [version 1; peer review: 2 approved with reservations]. NIHR Open Res 2026, 6:3 (https://doi.org/10.3310/nihropenres.15398.r39162) The direct URL for this report is: https://openresearch.nihr.ac.uk/articles/6-3/v1#referee-response-39162 https://openresearch.nihr.ac.uk/articles/6-3/v1#referee-response-39162 NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article. 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