1. Oxford Centre for Respiratory Medicine, Oxford University Hospitals National Health Service Foundation Trust, Oxford, United Kingdom
2. Unit of Health-Care Epidemiology, Big Data Institute, Li Ka Shing Centre for Health Information and Discovery, Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom
3. Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom
4. Oxford National Institute for Health Research Biomedical Research Centre, University of Oxford, Oxford, United Kingdom