1. Medical Research Council Integrative Epidemiology Unit; University of Bristol; Barley House, Oakfield Grove Bristol BS8 2BN U.K.
2. School of Social and Community Medicine; University of Bristol; Barley House, Oakfield Grove Bristol BS8 2BN U.K.
3. Department of Economics; University of Bristol; 8 Woodland Road Bristol BS8 1TN U.K.
4. Munich Center for the Economics of Aging; Max Planck Institute for Social Law and Social Policy; Amalienstr 33 80799 Munich Germany
5. Department of Public Health and Primary Care, School of Clinical Medicine; University of Cambridge; Cambridge CB1 8RN U.K.