Footnotes

• CF and NC contributed equally.

• Contributors All the authors have contributed to establishing the quality indicators by their participation in a thorough review of the relevant scientific literature.

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• 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 Commissioned; internally peer reviewed.