What is new?
Key findings There are many potential sources of complexity in the relationship between an intervention and its outcomes. There is also an increasing range of synthesis methods that can help with reviewing complex interventions. This article sets out how complexity can be taken into account when integrating evidence from qualitative and quantitative studies and sets out some of the main methodological options for integrating different types of evidence, and how they may shed light on intervention
What this adds to what was known?