Footnotes

• Contributors KS has written the manuscript and is the first and corresponding author. SH is the second author and has contributed to and critically appraised the manuscript. Neither author has any competing interests.

• 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.