Footnotes

• Handling editor Josef S Smolen

• Contributors The corresponding author had full access to all the data in the study, and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design: NP, AA, GP. Statistical analysis: NP, AA, GP. Interpretation of the data: NP, AA, GP. Drafting of the manuscript: NP, MDN, AA. Critical revision of the manuscript for important intellectual content: all authors. Final approval of the manuscript: all authors.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests MDN has received personal fees from Bayer, Daiichi Sankyo, Sanofi, Pfizer, Leo Pharma and Aspen, outside of the submitted work. AA has received research support from Novartis, Olatec and Swedish Orphan Biovitrum, outside of the submitted work.

• Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

• Patient consent for publication Not required.

• Provenance and peer review Not commissioned; externally peer reviewed.