What works for whom: a systematic review of inequalities in inclusion and effectiveness of social interventions for mental ill- health.

Purpose: People living with mental ill-health experience social and economic disadvantages, which contribute to poor outcomes and limit effectiveness of treatments. Interventions to improve social and economic circumstances have been developed, however, little is known about whether these interventions are effective for the most marginalised and disadvantaged groups, and those most in need of support.

Method: We conducted a systematic review in line with a pre-defined protocol to identify interventions to improve the social and economic circumstances of people experiencing mental ill-health. We included relevant records from two previous systematic reviews and updated their searches across four databases. We synthesised the intervention domains and locations of research, participant characteristics, and if effectiveness varied by participant gender, socioeconomic position, and race or ethnicity, and related indicators. We worked in partnership with an advisory board including those with relevant lived experience to conduct this work.

Results: We identified 266 relevant studies across 34 countries. Certain intervention domains were better researched than others (e.g. housing and employment vs. debt and social security advice). Participant characteristics were poorly reported resulting in a limited understanding of inclusiveness and generalisability of research. Only 8% of papers reported any stratified results and statistical reporting standards were poor, limiting our ability to determine what works for whom. Results from 4 RCTs indicated that interventions are less effective for those in lower socioeconomic groups.

Conclusion: Improved reporting and representation of marginalised groups, stratified analyses of intervention data, and replication of results is needed to confidently draw conclusions about what works for whom in this field.