Funding for this research was provided by:
Health Department and Finance Department of Guangdong Province (B2018237, A2016450)
Text and Data Mining valid from 2019-02-13
Received: 5 April 2018
Accepted: 2 February 2019
First Online: 13 February 2019
Compliance with ethical standards
: The authors have declared that they had no conflict of interests in relation to the work described. The authors have declared that they have had full control of all primary data and that they agreed to allow the Journal to review their data if requested.
: The present study is a meta-analysis and ethical approval is not needed for meta-analysis.