Funding for this research was provided by:
National High Technology Research and Development Program-863 of the Chinese Government
Text and Data Mining valid from 2018-06-18
Received: 22 August 2017
Accepted: 1 June 2018
First Online: 18 June 2018
Ethics approval and consent to participate
: It was approved by the Ethical Committee of Capital Medical University, Beijing, China. Data were obtained from a 2012 cross-sectional survey in urban Beijing. Written informed consent was obtained from each participant involved in this study. For participants under the age of eighteen, written informed consents were obtained from their guardians. All participants’ information was kept confidential and tracked anonymously with identification number only.
: The authors declare that they have no competing interests.
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