1. School of Health and Related Research (ScHARR), University of Sheffield, Sheffield, UK
2. Department of Psychology, University of Sheffield, Sheffield, UK
3. Department of Clinical Practice, University of Cork, Cork, Ireland
4. Centre for Research in Primary and Community Care, University of Hertfordshire, Hatfield, UK
5. Respiratory Department, Sheffield Children’s Hospital, Sheffield, UK
6. Clinical Practice Research Datalink, London, UK