1. School of Health and Health Related Research, University of Sheffield, Sheffield, UK
2. Division of Population Health, University of Sheffield, Sheffield, UK
3. The Department of Community Medicine, University of Jos, Jos, Nigeria
4. Medical Research Council Unit, The Gambia at the London School of Hygiene and Tropical Medicine, Faraja, The Gambia
5. School of Allied and Public Health Professions, Canterbury Christ Church University, Canterbury, UK