Footnotes

• Contributors The authors confirm contribution to the paper as follows: FM and AC were involved in study conception and data collection. FM, AC, CS, SP, MT and MB in analysis and interpretation of results. FM: manuscript preparation. All authors reviewed the results and approved the final version of 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.

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