Footnotes

• Contributors MP has sole accountability for all aspects of the work including conception, data acquisition and interpretation and has given final approval of the version to be published.

• 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.