Footnotes

• Contributors All authors conceived the study concept and study design. TH and SK performed complication and synthesis of the data. TH and SK carried out statistical analyses. TS supervised the research project. All authors participated in interpretation of the results and writing of the report, and approved the final version.

• 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 Obtained.

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