Funding for this research was provided by:
Research Grants Council of the Hong Kong Special Administrative Region, China (17126115)
Received: 10 October 2017
Accepted: 23 April 2018
First Online: 27 April 2018
Ethics approval and consent to participate
: Ethical approval for this study was obtained from the Institutional Review Board of the University of Hong Kong - West cluster Hospital authority (IRB No. UW 12–280). Written consent to participate in this study was obtained from every participant or parent.
: The authors declare that they have no competing interests.
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