Footnotes

• Contributors The author is solely responsible for the design, draft, revision and final approval of the work. The author agrees to be accountable for all aspects of the work.

• 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.

• Map disclaimer The depiction of boundaries on the map(s) in this article does not imply the expression of any opinion whatsoever on the part of BMJ (or any member of its group) concerning the legal status of any country, territory, jurisdiction or area or of its authorities. The map(s) are provided without any warranty of any kind, either express or implied.

• Competing interests None declared.

• Patient consent for publication Not required.

• Provenance and peer review Commissioned. Externally peer reviewed by Colin Mumford, Edinburgh, UK and David Simpson, Edinburgh, UK.