Footnotes

• Contributors GC conceived and designed the work. LCW, GC and FP analysed the data and drafted the first version of the text. EB reviewed and edited the work. All authors approved the final version of 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.