Footnotes

• Contributors All authors were involved in planning, writing and review of this paper.

• 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 and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

• Provenance and peer review Commissioned; externally peer reviewed.

• Author note References which include a * are considered to be key references.