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Contributors CJW: data collection, figures, data analysis and interpretation, manuscript drafting, critical revision of manuscript. OHIC: data analysis and interpretation, literature review, manuscript drafting, critical revision of manuscript. BC: study conception, study supervision, project planning, data interpretation, manuscript drafting, critical revision of 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 The authors declare no conflict of interest. No funding was received to assist with the preparation of this manuscript. OHIC was supported by the University of Hong Kong Summer Research Programme.
Provenance and peer review Not commissioned; internally peer reviewed.