Reducing friction, enabling response: a realist evaluation of a mobile outreach model for marginalized populations

Background: Mobile outreach initiatives have emerged to address persistent barriers to care for people experiencing homelessness, substance use, and mental illness. Although these models show promise, less is known about how and under what conditions they enable engagement and coordinated care. This study explains how, why, and under what circumstances a mobile, cross sector outreach model enables access to care for marginalized populations. Methods: We conducted a realist evaluation of Supportive Outreach Services (S.O.S.), a mobile, cross sector outreach program in Grey County, Ontario. Data included 31 semi structured interviews with outreach providers, partner organizations, system leaders, and clients, supplemented by document review and stakeholder feedback. Using retroductive reasoning and constant comparison, we developed and refined context mechanism outcome configurations to construct an explanatory program theory. Results: Five interconnected realist explanations account for how the model enables access to care. Trust built through repeated, non judgmental encounters supports engagement; proximity reduces barriers to participation; accessible support enables timely help seeking; cross sector relationships enable adaptive coordination; and visible results build legitimacy that sustains participation and resources. Together, these explanations provide a linked explanatory account of how mobile outreach reduces friction between marginalized populations and fragmented services while identifying the structural conditions that constrain its effectiveness. Conclusions: The effectiveness of mobile outreach depends less on the services delivered than on its capacity to reduce friction, sustain relationships, and adapt care across organizational boundaries. The resulting program theory offers transferable explanations for designing coordinated community based services while highlighting the structural conditions required for durable change.