Footnotes

• Handling editor Claudia S Estcourt

• Contributors DR designed the project. All authors contributed to data collection, analysis and final manuscript.

• 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.