Methodological Issues in Combining Diverse Study Types in Systematic Reviews

In this paper we discuss mixing methods at the level of reviews of research, combining the findings of multiple, already existing, studies that are labelled broadly as using either ‘qualitative’ or ‘quantitative’ methods. We define systematic reviews and outline the ‘mixed methods’ we have developed for combining diverse study types within them. Traditional systematic reviews usually answer a single question, use one type of study and, hence, only require one method of synthesis to combine the findings of studies. Our methods involve conducting three types of synthesis: (1) a statistical meta‐analysis to pool trials of interventions tackling a particular health, social or educational problem; (2) a synthesis of studies examining people’s perspectives or experiences of that problem using qualitative analysis; and (3) a mixed methods synthesis bringing the products of (1) and (2) together. We discuss the strengths of these mixed methods at the review level, reflect on their lessons for the concept of ‘triangulation’ and raise questions about the utility of the terms ‘qualitative’ and ‘quantitative’ and ‘mixed methods’ for classifying different types of research.