Footnotes

• Twitter @damian_roland

• Contributors DR: conceived the idea aided by data collated by KWT. SB, DL and EAG reviewed initial manuscripts, and all authors agreed a 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.

• Patient consent for publication Not required.

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