[1] Univ Bristol, Clin Trials & Evaluat Unit, Sch Clin Sci, Bristol BS2 8HW, Avon, England
[2] MRC, Biostat Unit, Cambridge CB2 2BW, England
[3] Univ York, Ctr Reviews & Disseminat, York YO10 5DD, N Yorkshire, England
[4] Univ Aberdeen, Hlth Serv Res Unit, Aberdeen, Scotland
[5] Inst Populat Hlth, Community Informat & Epidemiol Technol, Ottawa, ON, Canada
[6] Inst Populat Hlth, Ctr Global Hlth, Ottawa, ON, Canada
[7] Univ Ottawa, Dept Med, Ottawa, ON, Canada
[8] Univ Ottawa, Dept Epidemiol & Community Med, Ottawa, ON, Canada