Applying and reporting relevance, richness and rigour in realist evidence appraisals: Advancing key concepts in realist reviews.

The realist review/synthesis has become an increasingly prominent methodological approach to evidence synthesis that can inform policy and practice. While there are publication standards and guidelines for the conduct of realist reviews, published reviews often provide minimal detail regarding how they have conducted some methodological steps. This includes selecting and appraising evidence sources, which are often considered for their 'relevance, richness and rigour.' In contrast to other review approaches, for example, narrative reviews and meta-analyses, the inclusion criteria and appraisal of evidence within realist reviews depend less on the study's methodological quality and more on its contribution to our understanding of generative causation, uncovered through the process of retroductive theorising. This research brief aims to discuss the current challenges and practices for appraising documents' relevance, richness and rigour and to provide pragmatic suggestions for how realist reviewers can put this into practice.