[1] Univ Liverpool, Dept Biostat, MRC North West Hub Trials Methodol Res, Block F Waterhouse Bldg,1-5 Brownlow St, Liverpool L69 3GL, Merseyside, England
[2] Univ Liverpool, Clin Trials Res Ctr, Liverpool, Merseyside, England
[3] Univ Bristol, Bristol Randomised Trials Collaborat, Bristol, Avon, England
[4] Univ Edinburgh, Ctr Populat Hlth Sci, Edinburgh, Midlothian, Scotland
[5] UCL, Inst Clin Trials & Methodol, MRC Clin Trials Unit, London, England
[6] London MRC Hub Trials Methodol Res, London, England