Footnotes

• Contributors GF, RM and JH worked together on the original concept and design of the work. GF performed the data analysis and wrote the subsequent drafts with the other authors advising on the structure of the analysis, interpretation of results and edited drafts of the paper.

• Competing interests None.

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

• Data sharing statement There are more data, but this has not been published and there is no plan to publish it. It will be available to anyone with an interest in knowing more.