Table 2.

Subgroup analysis according to different doses, regions, and study designs

Subgroup	Covariate	Number of studies	Number of participants, N	I2 (%)	RR	95% CI	P
Overall	Adjusted	12	33,316	88	0.69	0.50–0.95	< 0.001
	Unadjusted	6	15,725	0	1.00	0.99–1.02	0.93
	Crude	18	49,041	87.4	0.80	0.68–0.93	< 0.001
Aspirin dose
80–100 mg/day	Adjusted	5	2615	44.3	0.64	0.48–0.85	0.002
	Unadjusted	1	10	NA	0.55	0.12–1.28	0.33
	Crude	6	2625	31.4	0.64	0.50–0.83	< 0.001
150 mg/day	Adjusted	1	183	NA	0.96	0.50–1.83	0.89
	Unadjusted	1	14,892	NA	0.96	0.89–1.04	0.30
	Crude	2	15,075	0	0.96	0.89–1.04	0.30
Unknown	Adjusted	6	30,518	93.9	0.76	0.43–1.34	0.34
	Unadjusted	4	823	0	1.00	0.99–1.02	0.77
	Crude	10	31,341	91.8	0.87	0.65–1.16	0.34
Region
Asia	Adjusted	7	12,994	29.1	0.79	0.56–1.12	0.19
	Unadjusted	3	795	0	1.00	0.99–1.02	0.77
	Crude	10	13,789	29.7	0.93	0.78–1.10	0.40
Europe and America	Adjusted	5	20,322	94.7	0.73	0.50–1.07	0.08
	Unadjusted	3	14,930	61.0	0.96	0.89–1.04	0.30
	Crude	8	35,252	93.0	0.71	0.52–0.98	0.04
Study design
Cohort study	Adjusted	9	32,350	90.7	0.73	0.52–0.99	0.04
	Unadjusted	2	322	0	1.00	0.99–1.02	0.78
	Crude	11	32,672	92.0	0.78	0.61–0.97	0.03
Case–control study	Adjusted	2	304	65.6	0.43	0.11–1.63	0.21
	Unadjusted	1	10	NA	0.55	0.17–1.83	0.33
	Crude	3	314	31.3	0.50	0.23–1.07	0.07
Cross-sectional study	Adjusted	1	662	NA	0.38	0.02–6.51	0.30
	Unadjusted	2	501	0	1.18	0.70–1.99	0.53
	Crude	3	1163	0	1.14	0.68–1.90	0.62
RCT	Unadjusted	1	14,892	NA	0.96	0.89–1.04	0.30

RR relative risks, 95% CI 95% confidence interval, RCT randomized controlled trial, NA not available

The italicized values indicates statistical significance