Footnotes

• Contributors DOM designed the systematic search terms, performed the search and subsequent paper selection, wrote the manuscript draft, and designed the figure and tables. IL identified the topic for systematic review, supervised the search strategy and paper selection, and revised the manuscript, figure and tables.

• 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.