Text and Data Mining valid from 2018-04-11
Received: 23 February 2017
Accepted: 21 March 2018
First Online: 11 April 2018
Ethics approval and consent to participate
: The study protocol was approved by Institutional Review Board of the University of Hong Kong/ Hospital Authority Hong Kong West Cluster (WU09–435) and written parental consent was obtained.
: Not applicable.
: The authors declare that they have no competing interests.
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