Peer review

Systematic reviews are increasingly used to inform policy makers about the usefulness of interventions. We stress the importance of the research question and argue that traditional Cochrane reviews work best for the focused question ‘what works’, while many policy interventions give rise to complex questions such as ‘when’, ‘why’, ‘how’ and ‘for whom’ the interventions ‘work’. We categorise the questions and use this as a basis for a typology of systematic reviews. We illustrate the usefulness of the typology by examining reviews of development interventions. These reviews have followed a general trend, moving from focused questions to complex questions, and this gives rise to the same problems and discussions about evidence-ranking and the use of programme theory as witnessed within systematic reviews of interventions in public health and education. We argue that the review question is a natural starting point for developing new practices for systematic reviews.

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