Jiang, Xiaofeng
He, Ping
Zhu, Dawei
Shi, Xuefeng
Meng, Qingyue
Article History
Received: 11 June 2020
Accepted: 18 November 2020
First Online: 10 December 2020
Ethics approval and consent to participate
: The study uses secondary data Collected by Health Commission of Shandong Province, and contains no individual information. Hence, ethical approval is not required.
: Not applicable.
: The authors declare that they have no competing interests.