Footnotes

• Contributors VB retrieved and analysed the data and prepared the draft manuscript. AES collated author comments and prepared the final manuscript. AES, VB, MW, JS and BW all contributed to the final article. VB and BW had supervising author input throughout the drafting of the 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.

• Provenance and peer review Not commissioned; internally peer reviewed.