Table 3.

Risk assessment results of bias included in case-control studies (score).

	Selection				Comparability	Exposure			Scores
	(1)	(2)	(3)	(4)	(5)	(6)	(7)	(8)
Zheng et al. (49)	1	1	1	1	1	0	1	0	6
Yuan (50)	1	1	1	1	2	0	1	0	7
Yang (51)	1	1	1	1	2	0	1	0	7
Liao et al. (52)	1	1	1	1	2	0	1	0	7
Tan (53)	1	1	1	1	2	0	1	0	7
Liu et al. (54)	1	1	1	1	2	0	1	0	7
Cen et al. (55)	1	1	1	1	2	0	1	0	7

(1) Is the case definition adequate? (2) Representativeness of the case. (3) Selection of controls. (4) Definition of controls. (5) Comparability of cases and controls on the basis of design or analysis. (6) Ascertainment of exposure. (7) Same method of ascertainment for cases and controls. (8) Non-response rate.