Conflict of interest: J.A. Krishnan reports research grants from US Patient Centered Outcomes Research Institute, American Lung Association, National Institutes of Health and COPD Foundation, consulting fees from AstraZeneca, CereVu Medical, BData, Inc. and American Board of Internal Medicine, payment or honoraria for lectures, presentations, manuscript writing or educational events from University of Chicago and American Academy of Asthma, Allergy, and Immunology, support for attending meetings and/or travel from National Institutes of Health, and participation in an observational safety monitoring board for National Institutes of Health; J.A. Krishnan is a member of the Board of Directors (unpaid) of the Respiratory Health Association and the Global Initiative for Asthma, and is a member of Medical and Scientific Advisory Committee (unpaid) for the COPD Foundation. R. Buhl reports research grants from Boehringer Ingelheim, GlaxoSmithKline, Novartis and Roche, payment or honoraria for lectures, presentations, manuscript writing or educational events from AstraZeneca, Berlin-Chemie, Boehringer Ingelheim, Chiesi, Cipla, GlaxoSmithKline, Novartis, Sanofi, Roche and Teva, and participation on a data safety monitoring board or advisory board for AstraZeneca, Berlin-Chemie, Boehringer Ingelheim, Chiesi, GlaxoSmithKline, Novartis, Sanofi and Roche; R. Buhl is a member of the GINA Science Committee (unpaid).