Footnotes

• Handling editor Josef S Smolen

• Contributors XP: design, acquisition and interpretation of the work, drafting of the work and approval of the final version. LD: acquisition and interpretation of the work, drafting of the work and approval of the final version. PB: design, acquisition and interpretation of the work, drafting of the work and approval of the final version.

• 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.

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