Footnotes

• Contributors RV had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. RV and VKB drafted the initial manuscript, analysed data and critically reviewed the final manuscript. Both authors contributed equally to the 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.

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