Conflict of interest: B. Lipworth reports grants, personal fees for consultancy, advisory board work and lectures, and expenses for meeting attendance from AstraZeneca and Chiesi, grants and personal fees for consultancy, advisory board work and lectures from Teva, provision of equipment from GSK, during the conduct of the study; personal fees for consultancy from Lupin, Cipla, Vectura, Dr Reddys and Glenmark, personal fees for advisory board work from Novartis, grants and personal fees for consultancy from Sanofi, outside the submitted work; and has a family member employed by AstraZeneca. Conflict of interest: R. Chan has nothing to disclose. Conflict of interest: C.R.W. Kuo reports personal fees for meeting attendance from AstraZeneca, personal fees for lectures and meeting attendance from Chiesi, personal fees for advisory board work from Circassia, outside the submitted work.