1. Consortium for Advanced Research Training in Africa (CARTA) , P.O. Box 10787, Nairobi 00100, Kenya
2. Centre for Health Policy, School of Public Health, Faculty of Health Sciences, University of the Witwatersrand , 51 2193, 60 York Rd, Parktown, Johannesburg 2193, South Africa
3. Health Economics Research Unit, KEMRI-Wellcome Trust Research Programme , 00100, Nairobi 00100, Kenya
4. Department of International Health, Johns Hopkins Bloomberg School of Public Health , 615 N Wolfe Street, E8143, Baltimore, MD 21205, USA