KEY MESSAGES
• Realist evaluation is a member of a family of theory-based evaluation approaches which begin by clarifying the ‘programme theory’: the mechanisms that are likely to operate, the contexts in which they might operate and the outcomes that will be observed if they operate as expected.
• Realist approaches assume that nothing works everywhere for everyone: context makes a big difference to programme outcomes. A realist evaluation asks not ‘what works?’ but ‘how or why does this work, for whom, in what circumstances?’
• Realist impact evaluation is most appropriate for evaluating new initiatives or programmes that seem to work but where ‘how and for whom’ is not yet understood; programmes that have previously demonstrated mixed patterns of outcomes; and those that will be scaled up, to understand how to adapt the intervention to new contexts.