1 Electronic Health Records Research Group, Faculty of Epidemiology and Population Health, London School of Hygiene & Tropical Medicine, London, WC1E 7HT, UK.
2 The DataLab, Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK.
3 The Phoenix Partnership, Horsforth, Leeds, UK.
4 Centre for Epidemiology Versus Arthritis, The University of Manchester, Manchester, UK.