1. Institute for Health and Aging, Department of Social and Behavioral Sciences, University of California , 490 Illinois Street, 12th Floor, Box 0646, San Francisco, CA 94158, USA
2. Division of Emergency Medicine, University of Cape Town , F51 Old Main Building, Groote Schuur Hospital, Observatory, Cape Town 7935, South Africa
3. Health, Nutrition and Population Global Practice, The World Bank , 1818 H Street, N.W., Washington, DC 20433, USA