1. Department of Primary Care and Public Health, Imperial College London, London W6 8RP, UK
2. Poole, UK
3. Faculty of Medicine, Imperial College London, London W6 8RP, UK
4. Department of Internal Medicine, American University of Beirut, Beirut 1107 2020, Lebanon
5. Department of Medicine, State University of New York at Buffalo, New York 14214, USA
6. Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada L8S 4L8