Footnotes

• Contributors The final manuscript was reviewed and approved by all authors, and they have taken care to ensure the integrity of the work. The material in this manuscript has not been published and is not being considered for publication elsewhere in whole or in part in any language.

• 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; externally peer reviewed.