1. Department of Clinical Gerontology, King’s College Hospital , London SE5 9RS , UK
2. Department of Sociology, Virginia Tech , Blacksburg, VA 24061 , USA
3. Department of Acute Medicine, Croydon University Hospital NHS Trust , London , UK
4. School of Medicine, University of Nottingham , Nottingham , UK
5. Department of Medicine for Elderly People, Whipps Cross University Hospital , London E11 1NR , UK
6. Gerontology Program, San Francisco State University , San Francisco, CA , USA