1. Department of Oral Health Policy and Epidemiology, Harvard School of Dental Medicine, Boston, MA, USA
2. Division of General Medicine and Clinical Epidemiology, University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, NC, USA
3. University College London, London, UK
4. London School of Economics, London, UK
5. Center for Primary Care and Outcomes Research and Center for Population Health Sciences, Departments of Medicine and of Health Research and Policy, Stanford University, Stanford, CA, USA
6. Center for Primary Care, Harvard Medical School, Boston, MA, USA
7. School of Public Health, Imperial College, London, UK