Mechanism-Based Middle-Range Theories: Using Realist Syntheses to Reconcile Specificity to Context and Generalizability.

Realist synthesis is a recognized methodological approach to evidence synthesis to inform evidence-based health policy and practice. The implicit assumption behind research synthesis is that the evidence it generates should be generalizable--drawing broad inferences from specific observations. While this understanding is generally shared among social scientists, tensions exist between having generalizable evidence and how this evidence can be useful in specific contexts. This paper considers the role of mechanism-based middle-range theories obtained from realist synthesis in bridging specificity to context and generalizability. Retroductive theorizing in realist synthesis helps to identify ideas about mechanisms related to the phenomenon embedded in the social and organizational contexts that could, in principle, have a much broader application. Also, because mechanism-based middle-range theories are linked to contextual features, they capture contextual nuances to enhance evidence implementation. We conclude that middle-range mechanisms provide an opportunity to achieve generalizability and contextualization in implementation science.