Footnotes

• Contributors AOG was responsible for helping to create the original research questions and analysis plan. GB wrote the first draft and conducted the analysis. KP and SDK contributed to the discussion and implications of the work. All authors contributed ideas, discussed the results and wrote the manuscript. All authors also approved the final version of the manuscript. AOG is the guarantor of 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.