Footnotes

• Contributors Both authors contributed equally to manuscript preparation, data gathering, final approval of the manuscript and finalising of the edited version.

• 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 Christian Lueck, Canberra, Australia.