[1] London Sch Hyg & Trop Med, Fac Epidemiol & Populat Hlth, Keppel St, London WC1E 7HT, England
[2] Univ Witwatersrand, Fac Hlth Sci, Sch Publ Hlth, Johannesburg, South Africa
[3] Ludwig Maximilians Univ Munchen, Inst Med Informat Proc Biometry & Epidemiol, Fac Med, Munich, Germany
[4] Univ Edinburgh, Usher Inst, Ctr Global Hlth, Edinburgh, Scotland
[5] Univ North Carolina, Gillings Sch Global Publ Hlth, Dept Hlth Behav, Chapel Hill, NC USA