Footnotes

• Handling editor Mary Frances McMullin.

• Contributors All authors have contributed to drafting, revision and approval of the manuscript. LA and HM are responsible for 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.