Footnotes

• Contributors Both authors contributed equally to the conception and design of the study, collection, analysis, and interpretation of the data, and drafting of the manuscript. All authors gave final approval of the manuscript for submission and publication and accept accountability for the study.

• 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.

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