If possible, a meta-analysis in fixed or random effects model will be conducted by R-3.5.1 software, otherwise a narrative synthesis will ensue focusing on prognostic factors. 
R-3.5.1 software
We will search seven electronic databases including the Cochrane Library, MEDLINE, EMBASE, Chinese BioMedical Database, China National Knowledge Infrastructure, Chinese VIP and Wangfang Database regardless of publication date or language. 
MEDLINE
We will search seven electronic databases including the Cochrane Library, MEDLINE, EMBASE, Chinese BioMedical Database, China National Knowledge Infrastructure, Chinese VIP and Wangfang Database regardless of publication date or language. 
EMBASE
We will search seven electronic databases including the Cochrane Library, MEDLINE, EMBASE, Chinese BioMedical Database, China National Knowledge Infrastructure, Chinese VIP and Wangfang Database regardless of publication date or language. 
Chinese BioMedical Database
We will search seven electronic databases including the Cochrane Library, MEDLINE, EMBASE, Chinese BioMedical Database, China National Knowledge Infrastructure, Chinese VIP and Wangfang Database regardless of publication date or language. 
China National Knowledge Infrastructure
We will search seven electronic databases including the Cochrane Library, MEDLINE, EMBASE, Chinese BioMedical Database, China National Knowledge Infrastructure, Chinese VIP and Wangfang Database regardless of publication date or language. 
Chinese VIP
We will search seven electronic databases including the Cochrane Library, MEDLINE, EMBASE, Chinese BioMedical Database, China National Knowledge Infrastructure, Chinese VIP and Wangfang Database regardless of publication date or language. 
Wangfang Database
We will search seven electronic databases including the Cochrane Library, MEDLINE, EMBASE, Chinese BioMedical Database, China National Knowledge Infrastructure, Chinese VIP and Wangfang Database regardless of publication date or language. 
Cochrane Library