Footnotes

• Contributors SK and DFK conceptualised and designed the study. MA collated the data. MA and XL analysed the data. MA and SK wrote the first draft of the manuscript. AJP, TT and DFK supervised the data collection and analysis, and critically reviewed the manuscript for important intellectual content.

• 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.