1. School of Geography and the Environment, University of Oxford , OX1 3QY, UK
2. Institute of Health Informatics, University College London , NW1 2DA, UK
3. Department of Geography and Planning, University of Liverpool , L69 3GP, UK
4. Demography Unit , Sociology Department, , 106 91 Stockholm, UK
5. Stockholm University , Sociology Department, , 106 91 Stockholm, UK
6. Department of Health Services Research and Policy, London School of Hygiene and Tropical Medicine , WC1H 9SH, UK