Systems-informed approaches to evaluating population health interventions: reflections from three case studies

There have been many calls for systems-informed approaches to evaluation. Population health interventions (PHI), which often focus on improving the upstream determinants of health through large-scale change, seem well-suited to systems-informed approaches to evaluation. The purported benefits and appropriateness of taking a systems-based approach to PHI evaluation have been extensively discussed and there is a growing, but still limited, number of applied case studies that operationalize these calls. Here, we reflect on insights gained from recent experiences across three evaluation case studies of: a late night levy to support local policing (UK), the tiered soft drinks industry levy (UK) and a value-based tax on sugar-sweetened beverages (Barbados). Building on theoretical work in this area, we illustrate through applied examples how a systems-informed approach can help to cast a wider net for potential impacts, be integrated with an effectiveness perspective to produce deeper insights, and support greater engagement with non-linearity.