Footnotes

• Contributors Data collection and/or processing, analysis and interpretation, manuscript writing: SFM. Manuscript writing and critiical review: NJ and DNR. Final approval: All authors.

• 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.