1. Usher Institute of Population Health Sciences and Informatics, The University of Edinburgh, Teviot Place, Edinburgh, EH8 9DX, Scotland.
2. Department of Service Delivery and Safety, World Health Organization, Geneva, Switzerland.
3. Health Systems and Innovation, World Health Organization, Geneva, Switzerland.
4. Department of Epidemiology and Public Health, London School of Hygiene & Tropical Medicine, London, England.