1. Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
2. School of Health Sciences, University of East Anglia, Norwich, UK
3. Department of Medicine, Dalhousie University, Nova Scotia, Canada
4. Division of Geriatric Medicine, Department of Medicine, Dalhousie University, Nova Scotia, Canada
5. Institute of Health and Society, Newcastle University Institute for Ageing, Newcastle University, Newcastle, UK
6. Department of Public Health and Primary Care, Cambridge Institute of Public Health, Cambridge, UK
7. MRC Biostatistics Unit, Cambridge University, Cambridge, UK