Footnotes Competing interests Professor Senn is a consultant to the pharmaceutical industry. Footnotes Competing interests All the authors have substantial involvement in the work of the Cochrane Collaboration. Footnotes Competing interests Dr Barnes has received research funding, sponsorship to attend meetings, and lecture fees from GlaxoWellcome; Mr Harris is employed by and Mr Hallett provides consultancy services to GlaxoWellcome. Footnotes Competing interests None declared. Footnotes Competing interests Professor Jadad is codirector of the Canadian Cochrane Network and Centre.