Table 2.

Subgroup analysis

Categories	N	Pooled RR	95% CI	P value	Heterogeneity
					I2	P′
Study design
Cohort	13	0.78	0.66–0.91	<0.001	90.4%	<0.001
Case-control	4	0.78	0.65–0.94	<0.001	0%	0.526
Cancer location
Colon	6	0.68	0.55–0.83	<0.001	86.2%	<0.001
Rectum	5	0.89	0.83–0.95	<0.001	0	0.887
Geographical region
America	3	0.58	0.46–0.74	<0.001	0	0.957
Europe	6	0.82	0.74–0.90	<0.001	51%	0.070
Asia	4	0.83	0.51–1.34	0.442	97%	<0.001

Abbreviations: N number of studies, RR relative risk, CI confidence intervals, P′ p value of I² statistics for heterogeneity