Footnotes

• Contributors SW and AB certify that neither this manuscript nor one with substantially similar content under our authorship has been published or is being considered for publication elsewhere. We have access to any data upon which the manuscript is based and will provide such data upon request to the editors or their assignees. We agree to allow the corresponding author to correspond with the editorial office, to review the uncorrected proof copy of the manuscript and to make decisions regarding release of information in the manuscript. We have given final approval of the submitted manuscript for which we take public responsibility for whole content. According to the definition given by the International Committee of Medical Journal Editors (ICMJE), we qualify for authorship based on making one or more of the substantial contributions to the intellectual content: conception and design, acquisition of data and analysis and interpretation of data. Furthermore, we have participated in drafting of the manuscript and critical revision of the manuscript for important intellectual content. SW is acting as the corresponding author.

• 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 consent for publication Obtained.

• Provenance and peer review Not commissioned; externally peer reviewed.