[1] Univ Oxford, Ctr Evidence Based Med, Dept Primary Hlth Care, Oxford OX3 7LF, England
[2] James Lind Lib, James Lind Initiat, Oxford OX2 7LG, England
[3] Univ London London Sch Hyg & Trop Med, London WC1E 7HT, England
[4] John Radcliffe Hosp, Nuffield Dept Surg, Oxford OX3 9DU, England