Footnotes

• Twitter @hirstposition, @GrossiIrene

• Contributors RH, HC, IG, CH, ATM-S and ES surveyed the literature and produced the research summaries. RH was responsible for organisation, editing, revisions and submission of this document.

• 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; internally peer reviewed.