Footnotes

• Correction notice This article has been corrected since it published Online First. A typographical error in the title has been corrected.

• Contributors MES designed the study, made the statistical analysis and drafted the manuscript. DCK provided access to the data. DCK and MJA assisted in the design and revised 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.

• 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 Not commissioned; internally peer reviewed.