Table 2.

Results of subgroup analyses and meta-regression based on study design

Type of IBD	Study design	RR (95% CI)	Heterogeneity	Number of studies	Number of participants	Subgroup differences	Residual heterogeneity
Crohn’s disease	Case-control	1.25 (1.05–1.50)	I2 = 89%	11	513,008	p = 0.24 REF	I2 = 69% R2 = 0% p < 0.0001
	Cohort	1.45 (1.23–1.71)	I2 = 82%	4	311,165	β 1.6 (95% CI−0.14 to 0.46)
Ulcerative colitis	Case-control	1.33 (1.24–1.42)	I2 = 89%	12	512,807	p = 0.78 REF	I2 = 91% R2 = 22% p < 0.0001
	Cohort	1.40 (0.99–1.98)	I2 = 94%	4	306,907	β −0.046 (95% CI −0.21 to 0.12)