Funding for this research was provided by:
The Research Grants Council of the Hong Kong Special Administrative Region, China (17115916)
Received: 31 August 2017
Accepted: 10 January 2018
First Online: 18 January 2018
Ethics approval and consent to participate
: The ethical approval of this study was granted by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster (UW 09-453).
: Not applicable.
: The authors declare that they have no competing interests.
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