[1] Univ Birmingham, Inst Appl Hlth Res, Publ Hlth Bldg, Birmingham B15 2TT, England
[2] Imperial Coll London, Sch Publ Hlth, London, England
[3] Univ Oxford, Nuffield Dept Primary Care Hlth Sci, Oxford, England
[4] London Sch Hyg & Trop Med, Dept Med Stat, London, England
[5] Univ Cambridge, MRC Biostat Unit, Cambridge, England
[6] Univ Edinburgh, Coll Med & Vet Med, Edinburgh, Scotland