Footnotes

• Contributors DS: conception and design, drafting of the manuscript, revising the manuscript critically for important intellectual content and final approval of the submitted version. LR: drafting of the manuscript, revising the manuscript critically for important intellectual content and final approval of the submitted version. AM: revising the manuscript critically for important intellectual content and final approval of the submitted 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.