1. ECOHOST—Centre for Health and Social Change, London School of Hygiene and Tropical Medicine, London WC1H 9SH, UK
2. Department of Health Services Research, CAPHRI, Maastricht University, Maastricht, The Netherlands
3. Norwich Medical School, University of East Anglia, Norwich NR4 7TJ, UK
4. Department of Sociology, Oxford University, Oxford OX1 3UQ, UK