Footnotes

• Twitter @No twitter

• Contributors AT, TB and DOD designed the question. MM conducted the literature search. All authors reviewed the evidence and contributed to the writing and review of the 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; internally peer reviewed.