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Stephanie Tierney and Kamal R Mahtani discuss meta-synthesis and its role for patients, practitioners and policy makers.

Systematic reviews of quantitative research are a staple of decision-making for those providing and commissioning services. They often provide systematically derived answers to questions like: Does this treatment work? How accurate is this test? How common is this problem? They do this by bringing together all evidence (as far as possible) addressing a specific review topic.

However, evidence users often have queries that cannot be answered by pooling numerical data; questions concerned with the implementation of evidence into practice or designing services that are patient-centred. Such questions may be more related to: Why and how did the treatment work? How acceptable is this test likely to be in my population?

A meta-synthesis can help to answer such questions, adding a different layer of knowledge to a quantitative review. In a meta-synthesis, findings from qualitative research are compared, contrasted and combined. This enables researchers to provide a more nuanced understanding of phenomena or to produce a new concept or theory by reading and reinterpreting existing literature. Meta-syntheses can highlight barriers and enablers to an intervention’s implementation. Alternatively, they may focus on people’s experiences of living with a condition, or offer an insight into the meaning associated with, for example, medication or other elements of treatment.

The complementarity of quantitative and qualitative reviews was highlighted in a project reported by Thomas and colleagues (2004), which explored the topic of fruit and vegetable intake among children. It included a meta-analysis of controlled trials and a thematic synthesis of studies on children’s views/perceptions. Trial data suggested interventions were able to increase fruit and vegetable intake by half a portion a day on average. However, heterogeneity was noted among the trials. Qualitative data highlighted barriers and facilitators to fruit and vegetable intake, and offered an insight into why some interventions may be more or less effective than others at improving children’s eating behaviour.

Having a good grasp of the purpose and scope of meta-syntheses is important for researchers, but also for individuals funding services, writing policy and providing care. With this in mind, we have developed a one-day course on qualitative systematic reviewing; an introduction to the topic for those who want to learn more. It takes place on 2nd July 2019 at the University of Oxford. For more details, please visit the Centre for Evidence Based Medicine’s website.