Text and Data Mining valid from 2019-05-29
Received: 16 October 2018
Accepted: 14 April 2019
First Online: 29 May 2019
Compliance with ethical standards
: The CNFS was approved by the Institutional Review Board of the 3rd Hospital of Hebei Medical University. Written informed consent was obtained from each participant before data collection.
: The authors declare that they have no competing interests.