Footnotes

• Contributors SMC and GC collaborated in the planning, conduct, reporting, conception and design, acquisition of data or analysis and interpretation of data. Both authors read and approved the final 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.

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