Qualitative evidence synthesis is a process of combining evidence from individual qualitative studies to create new understanding by comparing and analysing concepts and findings from different sources of evidence with a focus on the same topic of interest. Therefore, qualitative evidence synthesis can be considered a complete study in itself, comparable to any meta-analysis within a systematic review on effects of interventions or diagnostic tests. It can be an aggregative or interpretive process but requires transparency of process and requires authors to identify and extract evidence from studies included in the review; to categorize the evidence; and to combine these categories to develop synthesized findings. In undertaking this methodological work, however, it is important to recognize that the real prize from the synthesis of qualitative evidence is not just a description of how people feel about an issue or treatment but an understanding of ‘why’ they feel and behave the way they do (Popay 2005).
For example, primary qualitative research on the experience of chronic illness presents people’s accounts of the onset of their illness. But this body of work also moves beyond description to seek to explain the social purpose of these accounts – showing how through these narratives people ‘reconstruct’ a sense of worth in a social context in which all illness has moral overtones (Williams 1984). Similarly, a recent systematic review of qualitative research on medicine taking (Campbell 2003, Pound 2005) utilizing meta-ethnography as a method for synthesis moves beyond providing a summary of recurring ‘themes’ across studies to build an explanation of why people use medication (or not) in the way they do.