Footnotes

• Contributors Conception of the work—PGBR, TTdL and PRN. Drafting the work—PGBR, TTdL and PRN. Acquisition of the data—TTdL and FBD. Analysis and interpretation of data for the work—all authors. Design of the work—FBD and PRN. Revising the work critically—FBD and PRN. Final approval of the version to be published and agreement to be accountable for all aspects of the work—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. Externally peer reviewed by Jeremy Rees, London.

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