1 Research in Real-Life, Cambridge, UK; Academic Primary Care, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen AB25 2ZD, UK. Electronic address: dprice@rirl.org.
2 Respiratory Medicine Unit, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
3 Primary Care and Population Sciences, and NIHR Southampton Respiratory Biomedical Research Unit, University of Southampton, Southampton, UK.
4 King's College London, London, UK.
5 Norwich Medical School, University of East Anglia, Norwich, UK.