Footnotes

• Twitter @MariaParekh

• Contributors All authors contributed equally to the conception and design, acquisition of data or analysis and interpretation of data, and approved the final version for publication. CDLG and MAP drafted the article, and MAP and JJ revised it critically for important intellectual content. The corresponding author, MAP, takes full responsibility for the data, interpretation and the conduct of the research; has full access to all of the data; and has the right to publish any and all data separate and apart from any sponsor.

• 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.