Footnotes

• Contributors QP, CK and MR had full access to all data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Concept and design: CK and MR. Acquisition, analysis or interpretation of data: QP, AC, AD, AG, CK and MR. Drafting of the manuscript: QP and MR. Critical revision of the manuscript for important intellectual content: All. Statistical analysis: QP and CK. Obtained funding: NA. Administrative, technical or material support: None.

• 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.