Table 2. Subgroup analysis.

Subgroup	No. of studies	Odds Ratio (95%CI)	P value	I2	P for heterogeneity
All	5	1.33(0.91,1.93)	0.138	73.0	0.005
Case control study	3	0.79(0.23,2.63)	0.696	86.1	0.001
Retrospective cohort study	2	1.48(1.22,1.80)	<0.001	0.0	0.403
Sample size(>2000)	3	1.60(1.35,1.89)	<0.001	37.2	0.203
Sample size(≤2000)	2	0.48(0.25,0.91)	0.025	39.1	0.200
Follow up time(>10 years)	3	1.27(0.87,1.86)	0.207	68.1	0.044
Follow up time(≤10 years)	2	0.69(0.05,8.88)	0.777	84.2	0.012