Footnotes

• Correction notice The following sentence has been corrected since it was first published: "The multivariate analysis revealed a lower mortality risk (relative risk 0.39, 95% CI CI 0.32 to 0.48, p<0.01)".

• Contributors DV wrote the initial drafts. PPB, GC and JLM edited the drafts. All authors approved the final 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.

• Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting or dissemination plans of this research.

• Provenance and peer review Commissioned; externally peer reviewed.