[1] City Univ London, Sch Hlth Sci, Myddelton St Bldg,1 Myddelton St, London EC1R 1UW, England
[2] Imperial Coll London, Sch Publ Hlth, Imperial Clin Trials Unit, Stadium House,68 Wood Lane, London W12 7RH, England
[3] St Georges Univ London, Populat Hlth Res Inst, Cranmer Terrace, London SW17 0RE, England
[4] Kings Coll London, Inst Psychiat Psychol & Neurosci, Hlth Serv & Populat Res Dept, London SE5 8AF, England
[5] St Georges Univ London, Ctr Technol Educ, Cranmer Terrace, London SW17 0RE, England
[6] Univ Liverpool Liverpool Sch Trop Med, Dept Clin Sci, Pembroke Pl, Liverpool L3 5QA, Merseyside, England