Footnotes

• Handling editor Mary Dixon-Woods

• Contributors The project was initiated and led by JG and AlM. All four authors made substantial contributions to the design of the work and the acquisition, analysis and interpretation of data. JG drafted the paper, but all four had a hand in revising it critically for important intellectual content and gave final approval of the version submitted. All agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

• Competing interests None declared.

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