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Results of quality assessment of included studies
(a) Risk of bias in each study. (b) Overall result of each item in quality assessment. DcZhu2011C, DcZhong2011L, DcZhang2011C, DcYuan2013L, DcYuan2011L, DcYuan2011C, DcSheng2011L, DcRen2013B, DcNi2013B, DcLi2012C, DcLi2009L, and DcGao2014G represent the studies as shown in Table 1
