1. Health Economics Unit, School of Public Health and Family Medicine, Health Sciences Faculty, University of Cape Town, Anzio Road, Observatory, Cape Town 7925, South Africa,
2. School of Public Health and Community Medicine, University of New South Wales, Kensington, NSW, Australia,
3. Khon Kaen University, Khon Kaen, Thailand, and
4. Department of Global Health and Development, London School of Hygiene and Tropical Medicine, London, UK