Text and Data Mining valid from 2018-07-16
Received: 20 March 2018
Accepted: 4 July 2018
First Online: 16 July 2018
Ethics approval and consent to participate
: Ethical approval for data collection was obtained at Peking University and updated annually. Approval for this study was given by the medical ethics committee of Health Science Center of Xi’an Jiaotong University (approval number 2015–642). All respondents gave written informed consent prior to data collection.
: Not applicable.
: The authors declare that they have no competing interests.
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