Footnotes

• Twitter @allthingssmall8

• Contributors EA conducted the relevant literature search. Both authors appraised the evidence. AS devised the manuscript and also made necessary revisions. AS responded to queries of reviewers. All authors agreed on the final submission format.

• 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; externally peer reviewed.