[1] Univ York, Ctr Hlth Econ, York YO10 5DD, England
[2] Imperial Coll, Business Sch, London, England
[3] Univ Witwatersrand, Dept Internal Med, Hlth Econ & Epidemiol Res Off, Fac Hlth Sci, Johannesburg, South Africa
[4] Univ Witwatersrand, Fac Hlth Sci, Sch Publ Hlth, Johannesburg, South Africa
[5] Duke NUS Med Sch, Hlth Serv & Syst Res, Singapore, Singapore
[6] Univ Washington, Comparat Hlth Outcomes Policy & Econ Inst, Dept Pharm, Seattle, WA USA