Footnotes

• Contributors UK: provided and analysed the data, drafted, revised and approved the manuscript. AKS: provided and analysed the data, revised and approved the manuscript. JT: provided and analysed the data, revised and approved the 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.