Footnotes

• Twitter @davidnnaumann

• Contributors EK initiated the project and collected the data. Data analysis was undertaken by EK and interpreted by DNN and DMB. EK wrote the first draft of the manuscript, and DNN and DMB provided critical appraisal and revisions. All authors 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.

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