Footnotes

• Handling editor Anna Maria Geretti

• Contributors CCC designed the data collection tools, monitored the data collection, wrote the statistical analysis plan, cleaned and analysed the data, and drafted and revised the paper. JRG and OAS analysed the data, and drafted and revised the paper. DC, MF and MRS revised the draft paper. SK monitored the data collection and revised the draft paper.

• 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.

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