Thus far, most systematic reviews commissioned to inform international development policy have focused on questions of 'what works', drawing on experimental and quasiexperimental studies of the effects of interventions. This article argues that systematic review methods can be applied to answer a range of different questions for international development and pays particular attention to methods of synthesising qualitative evidence that apply the key principles of systematic reviewing of being comprehensive, systematic and transparent. The article introduces readers to the types of questions for which reviews of qualitative evidence might be appropriate, the types of evidence such reviews might include and the range of methods available for their synthesis.Keywords: systematic review; qualitative synthesis; evidence-based policy; narrative synthesis; development effectiveness IntroductionOver the last decade, there has been an increased focus on enhancing the use of evidence to inform international development policy and practice. Donors, implementing agencies and governments are under increasing pressures to demonstrate that their policies are informed by evidence. This has led to an increase in the demand for systematic reviews of the evidence pertaining to a range of different areas of policy with relevance to low-and middle-income countries.Thus far, most systematic reviews commissioned to inform international development policy have focused on questions of 'what works', drawing on experimental and quasiexperimental studies of the effects of interventions. However, such reviews are increasingly criticised for being too narrow and 'rigid', failing to address other important questions such as, for instance, why a particular interventions work or not (Mallett et al. 2012). Moreover, a number of reviews of effectiveness have been inconclusive due to a lack of evidence on effects and there are rising concerns that useful evidence on other questions is being overlooked (Snilstveit 2012).A narrow focus on effectiveness when policy-makers need answers to a range of questions beyond 'what works' is rightly criticised, although this is not a limitation of systematic review methodology per se. The principles underpinning systematic review methodology can be applied to answer a range of different questions, and include the synthesis of a range of different types of evidence, including qualitative evidence (Petticrew and Roberts 2006,

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The Campbell Collaboration was founded on the principle that systematic reviews on the effects of interventions will inform and help improve policy and services. Campbell offers editorial and methodological support to review authors throughout the process of producing a systematic review. A number of Campbell's editors, librarians, methodologists and external peer reviewers contribute. Plain language summaryInterventions to reduce homelessness and improve housing stability are effectiveThere are large numbers of homeless people around the world. Interventions to address homelessness seem to be effective, though better quality evidence is required. What is this review about?There are large numbers of homeless people around the world. Recent estimates are over 500,000 people in the USA, 100,000 in Australia and 30,000 in Sweden. Efforts to combat homelessness have been made on national levels as well as at local government levels.This review assesses the effectiveness of interventions combining housing and case management as a means to reduce homelessness and increase residential stability for individuals who are homeless, or at risk of becoming homeless. What is the aim of this review?This Campbell systematic review examines the effectiveness of interventions to reduce homelessness and increase residential stability for individuals who are homeless, or at risk of becoming homeless. Forty-three studies were included in the review, 37 of which are from the USA. What studies are included?Included studies were randomized controlled trials of interventions for individuals who were already, or at-risk of becoming, homeless, and which measured impact on homelessness or housing stability with follow-up of at least one year.A total of 43 studies were included. The majority of the studies (37) were conducted in the United States, with three from the United Kingdom and one each from Australia, Canada, and Denmark. 6The Campbell Collaboration | www.campbellcollaboration.org What are the main findings of this review?Included interventions perform better than the usual services at reducing homelessness or improving housing stability in all comparisons. These interventions are: These interventions seem to have similar beneficial effects, so it is unclear which of these is best with respect to reducing homelessness and increasing housing stability. What do the findings of this review mean?A range of housing programs and case management interventions appear to reduce homelessness and improve housing stability, compared to usual services.However, there is uncertainty in this finding as most the studies have risk of bias due to poor reporting, lack of blinding, or poor randomization or allocation concealment of participants. In addition to the general need for better conducted and reported studies, there are specific gaps in the research with respect to: 1) disadvantaged youth; 2) abstinence-contingent housing with case management or day treatment; 3) non-abstinence contingent housing comparing group vs independent living; 4) Hous...

We provide a 'how to' guide to undertake systematic reviews of effects in international development, by which we mean, synthesis of literature relating to the effectiveness of particular development interventions. Our remit includes determining the review's questions and scope, literature search, critical appraisal, methods of synthesis including meta-analysis, and assessing the extent to which generalisable conclusions can be drawn using a theory-based approach. Our work draws on the experiences of the International Initiative for Impact Evaluation's (3ie's) systematic reviews programme.

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