Contextual factors in systematic reviews: understanding public health interventions in low socioeconomic status and disadvantaged populations

BACKGROUND: Evaluations of public health interventions require an understanding of the contextual factors that shape their effectiveness. Context (including socioeconomic, cultural, and environmental factors) plays a critical role in establishing how interventions achieve impact, why outcomes can vary and whether the interventions of interest can be translated from one context to another. This overview explores the extent to which systematic reviews of public health interventions for low-income or low socioeconomic status (SES) populations report contextual factors influencing outcomes. METHODS: Systematic reviews were identified through a scoping review and updated searches in March 2023. Reviews focused on interventions targeting smoking, unhealthy diet, physical inactivity, and harmful alcohol use in disadvantaged groups. Reviews were screened for eligibility, and data were extracted on contextual factors related to intervention implementation and effectiveness. Data were synthesised using a framework approach, categorising findings by behaviour and level of intervention. RESULTS: Applying a very broad definition of context, 29 of 86 identified reviews provided some degree of contextual data which varied across interventions but was largely restricted to intervention implementation and delivery factors. For example, environmental characteristics, such as crime and perceived personal safety, affected the use of physical activity infrastructure in disadvantaged areas. Food voucher schemes had mixed results, with social and economic factors affecting their use and effectiveness. However, most reviews lacked sufficient reporting on contextual data, limiting conclusions on the role of context in intervention outcomes. CONCLUSIONS: Contextual factors are often underreported in systematic reviews of public health interventions targeting disadvantaged populations. Such underreporting is likely to be similar in other areas of public health. This limits policymakers' ability to adapt interventions to specific settings. Improved reporting and consideration of context in systematic reviews are needed to ensure that interventions are appropriately tailored to the needs of low-income and low SES groups.