Over the last 25 years, meta-analysis has been widely used to study the effects of practical treatment interventions in fields ranging from psychology and education to medicine and public health. The present article first describes the impact of meta-analysis. The article then presents a description of some preliminary results of a study of the main design characteristics of published interventions in Europe. In order to foster both better experimental designs and more systematic reviews in the European context, and to promote collaboration between different countries and research groups, the authors then describe and discuss the Campbell Collaboration (C2), a new international organization aimed at fostering public policies and practices based on systematic reviews of high-quality evidence. Though there is some overlap between the work of the Campbell Collaboration and its sibling organization the Cochrane Collaboration, Campbell focuses more on systematic reviews in the social, behavioral and educational areas. Reviewers in those areas encounter difficulties over the use of non-randomized designs, difficulties in effect-size computation, and the need for new computer software to better serve the needs of meta-analytic reviews in the social sciences.
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