Footnotes

• Contributors VP conceptualised the study, undertook the data extraction, prepared the draft manuscript and contributed to the final submission of the study. DS contributed to the manuscript preparation and reviewed the 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.

• Patient consent for publication Not required.

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