Using financial incentives to improve health service engagement and outcomes of adults experiencing homelessness: A scoping review of the literature.

People experiencing homelessness (PEH) have high rates of acute and chronic health conditions, complex support needs and often face multiple barriers to accessing health services. Financial incentive (FI) interventions have been found effective in improving service engagement and health outcomes for a range of health conditions, populations and settings, but little is known about their impact on PEH. We conducted a scoping review to explore the impact of FI interventions on treatment retention, adherence and other health outcomes of PEH. We searched seven electronic databases from inception to September 2021 to identify peer-reviewed published English language studies that used FI interventions with adult PEH. A scoping review methodology was used to chart relevant data uniformly. Descriptive statistics and narrative syntheses were used to describe outcomes. Thirty-three quantitative articles related to 29 primary studies were published between 1990 and 2021 and met inclusion criteria. Studies targeted three areas of health behaviour change: decreasing substance use or increasing abstinence rates, preventing or treating infectious diseases or promoting lifestyle/general health goal attainment. A variety of FIs were used (cash/non-cash, escalating/fixed schedule, larger/smaller amounts, some/all behaviours rewarded, certain/uncertain reward) across studies. Twenty-six of the primary studies reported significantly better outcomes for the participants receiving FI compared to controls. There were mixed findings about the efficacy of cash versus non-cash FIs, non-cash FIs versus other interventions and higher versus lower value of incentives. Furthermore, there was limited research about long-term outcomes and impacts. FIs have promise in increasing abstinence from substances, engagement in infectious disease treatment, retention in health services and general lifestyle modifications for PEH. Future research should examine long-term impacts and the contribution of co-interventions and intermediary lifestyle behaviour changes.