1. Department of Sociology, Oxford University, Manor Road Building, Manor Road, Oxford OX1 3UQ, UK
2. Faculty of Public Health & Policy, London School of Hygiene & Tropical Medicine, London WC1E 7HT, UK
3. MRC/CSO Social & Public Health Sciences Unit, University of Glasgow, Glasgow G12 8QQ, UK
4. Department of Public Health and Policy, University of Liverpool, Liverpool L69 3BX, UK