1. Centre for Evidence-Based Medicine, University of Oxford, OX2 6HX, UK
2. Department of Mathematics, Aston University, Birmingham, B4 7ET, UK
3. Institute for Evidence Based Healthcare, Bond University, Queensland, QLD 4226, Australia
4. Universite Paris Cite and Universite Sorbonne Paris Nord, Inserm, INRAE, Centre for Research in Epidemiology and Statistics (CR ESS), F-75004 Paris, France
5. 2 Reading Road, Wallingford OX10 9DP, UK