1. Nuffield Department of Population Health, University of Oxford, Oxford OX3 7LF, UK
2. MRC Biostatistics Unit, University of Cambridge, Cambridge CB2 0SZ, UK
3. MRC Integrative Epidemiology, University of Bristol, Bristol BS1 3NY, UK
4. Population Health Sciences, Bristol Medical School, University of Bristol, Bristol BS1 3NY, UK
5. Department of Preventive Medicine, The University of Tennessee Health Science Center, Memphis, TN 38163, USA