1. Barts and The London School of Medicine and Dentistry and Institute of Dentistry, Queen Mary University of London, London E1 2AT, UK
2. Department of Primary Care and Public Health, Imperial College London, London W6 8RP, UK
3. Academic Unit of Primary Care and Population Sciences, University of Southampton, Southampton SO16 6YD, UK
4. Department of Internal Medicine, American University of Beirut, Beirut, Lebanon
5. Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada