Footnotes

• Contributors KM conceptualised and designed the paper and reviewed, revised and edited the manuscript for important intellectual content. BS drafted the initial manuscript. Both authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.

• 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 Commissioned; externally peer reviewed.