Footnotes

• Contributors EM was responsible for project concept and design, acquisition of data, manuscript preparation and critical revision of manuscript for intellectual content. RG critically revised the manuscript for intellectual content and was involved in supervision of the project. DH critically revised the manuscript for intellectual content and was involved in supervision of the project. MR critically revised the manuscript for intellectual content and was involved in supervision of the project. ML critically revised the manuscript for intellectual content and was involved in supervision of the project. DGM critically revised the manuscript for intellectual content and was involved in supervision of the project. SC critically revised the manuscript for intellectual content and was involved in supervision of the project. NFC critically revised the manuscript for intellectual content and was involved in supervision of the project. RR was involved in project concept and design, critical revision of manuscript for intellectual content and project supervision.

• Competing interests None declared.

• Provenance and peer review Commissioned; externally peer reviewed. This paper was reviewed by Georgina Burke, Southampton, UK.