1. Division of Population, Health Sciences and Education, St George’s, University of London, London, UK
2. Social Science Research Unit, Faculty of Children and Learning, Institute of Education, London, UK
3. School of Social and Community Medicine, University of Bristol, Bristol, UK
4. Peter Jordan Associates, London, UK
5. Department of Health Services Research and Policy, Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine, London, UK