1. Centre for Health Services Research, University of Newcastle upon Tyne, UK
2. Department of Medicine (Geriatrics) and Department of Epidemiology and Public Health, University of Newcastle upon Tyne, Newcastle upon Tyne, UK
3. Academic Section of Geriatric Medicine, Royal Infirmary, Glasgow, Newcastle upon Tyne, UK
4. Centre for Health Services Research, University of Newcastle upon Tyne, Newcastle upon Tyne, UK