Footnotes

• Contributors WS conceptualized and designed the study, drafted the initial manuscript, participated in literature retrieval, collected data, carried out the initial analyses, and reviewed and revised the manuscript. YR participated in literature retrieval, collected the data, carried out the initial analyses, and reviewed and revised the manuscript. XZ and HY conceptualized and designed the study, coordinated and supervised data collection, and critically reviewed the manuscript for important intellectual content. All authors approved the final manuscript as submitted and agreed to be accountable for all aspects of the work.

• 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; internally peer reviewed.