Funding for this research was provided by:
Program of Natural Science Fund of China (81773512)
National Key Basic Research Project of China (2016YFC0207705)
Text and Data Mining valid from 2019-08-01
Received: 1 October 2018
Accepted: 12 July 2019
First Online: 1 August 2019
Ethics approval and consent to participate
: Because this study used secondary data and did not involve human subjects directly, informed consent was not obtained from the patients. However, confidentiality was only necessary when handling the retrieved data from the Beijing Public Health Information Center in the study. Data obtained from the Beijing Public Health Information Center are stored until the Capital Medical University gives permission for its use. We obtained ethical approval from the ethics review committee of the Capital Medical University, Beijing, China.
: Not applicable.
: The authors declare that they have no competing interests.