Table 3.

Quality assessment for all the included studies of the CAD

First author	Publishing year	Selection	Comparability	Exposure
Jiao [15]	2007	☆☆☆	☆☆	☆☆☆
Huang [14]	2009	☆☆☆	-	☆☆☆
Zheng [22]	2009	☆☆☆	☆	☆☆☆
Ma [16]	2011	☆☆	☆	☆☆
Zhang [23]	2012	☆☆☆☆	-	☆☆
Wang [19]	2009	☆☆☆	-	☆☆