Footnotes

• Handling editor Josef S Smolen

• Contributors All authors were involved in drafting the manuscript or revising it critically, and approved the final version. CS had full access to all the data in the study and takes responsability for the integrity of the data and accuracy of the data analysis. Study design: CS, GB, EG, FM, LB, MC, NP, GC, NG, SC, MB, VDL, GD, MM, AMM, MC, PGR. Statistical analysis: PM, MC, PGR. Data Collection: CS, GB, EG, FM, LB, MC, NP, GC, NG, SC, MB, VDL, GD, MM, AMM, MC, PGR.

• 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 None declared.

• 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.