Table 1. Main results of overall and subgroups in the meta-analysis.

Overall and subgroups analyses	No. of studies	OR	95% CI	Heterogeneity
				P value	I2 (%)
Total	42	0.95	0.87–1.04	<0.001	52.6
Total *	39	0.96	0.90–1.01	0.17	17.8
Ethnicity
Asian	9	0.95	0.80–1.03	0.55	0.00
Caucasian	19	0.94	0.87–1.02	0.04	39.6
Mixed	10	0.97	0.89–1.07	0.44	0.20
Source of controls
Population based	37	0.98	0.89–1.07	0.001	52.8
Hospital based	4	0.79	0.53–1.16	0.44	0.00
Genotyping methods
PCR-RFLP	20	0.98	0.87–1.10	0.04	39.8
PCR-RFLP/(AS)-PCR	3	0.81	0.57–1.16	0.39	0.00
F-based melting curve	2	0.87	0.70–1.09	0.78	0.00
TaqMan	4	0.72	0.46–1.12	<0.001	89.0
Gender
Male	6	1.16	0.95–1.42	0.94	0.00
Female	6	1.03	0.74–1.42	0.04	57.1
Smoking status
Never smoke	5	0.93	0.66–1.32	0.01	69.8
Ever smoke	6	0.89	0.69–1.15	0.07	51.9
Tumor site
Colon cancer	3	0.91	0.80–1.05	0.86	0.00
Rectal cancer	3	1.07	0.92–1.24	0.77	0.00

^*Three studies excluded for exploring the source of heterogeneity. [23], [25], [36], confidence interval, CI.