Justification, rationale and methodological approaches to realist reviews

Realist reviews offer a method to understand why an intervention is successful or not. Many factors influence how complex healthcare interventions are delivered and this makes understanding what works difficult. Effectiveness depends on delivery context, and success in one setting does not guarantee the same result in alternate settings. How an intervention works (the underlying mechanisms) in a particular setting for one population group, may not work in the same way for a different group. A realist review provides an iterative theory-driven approach to help understand how and for whom and under what conditions an intervention works.