The role of systematic reviews of qualitative evidence in evaluating interventions: a case study.

Systematic reviews of qualitative evidence have been widely used to provide information on the context and implementation of interventions, and their potential barriers and facilitators. However, such reviews face a number of methodological challenges, and there are ongoing debates as to how qualitative evidence can best be used to inform our understanding of interventions. In this paper, we use a case study of two systematic reviews of qualitative evidence on the prevention of skin cancer to explore these issues. We find that qualitative evidence not directly related to interventions is likely to be of value for such reviews, that it is often not possible to construct fully comprehensive search strategies, and that there are diminishing returns to the synthesis, in terms of added value or insight, from the inclusion of large numbers of primary studies. We conclude that there are a number of ways in which systematic reviews of qualitative evidence can be utilised in conjunction with evidence on intervention effectiveness, without compromising the rigour of the review process. In particular, the use of theory to inform frameworks for synthesis is a promising way to integrate a broader range of qualitative evidence.