Funding for this research was provided by:
Opening Foundation (KF-01-115,NCRCG-PLAGH-2017017)
National Natural Science Foundation of China (81703285)
Beijing Natural Science Foundation (7174350)
Beijing Municipal Science and Technology Commission (Z161100005016021)
Beijing Nova Program (Z181100006218085)
Military Fund (15BJZ41, 17BJZ51)
Article History
Received: 28 May 2018
Accepted: 3 January 2019
First Online: 15 January 2019
Ethics approval and consent to participate
: The use of CLHLS data was approved by the Biomedical Ethics Committee of Peking University, and written informed consent was obtained from each respondent.
: Not applicable.
: The authors declare that they have no competing interest.
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