Table 2. Analyses of outcomes by categories.

Outcome	No. of studies	Participants	Statistical model	Effect estimate (95% CI)
Stage I vs. II-IV	6	2315	Random-effects	0.84 (0.74, 0.96)
T1 vs. T2-4	11	26570	Random-effects	0.82 (0.77, 0.87)
N0 vs. N1-3	8	24763	Fixed-effect	0.85 (0.83, 0.87)
G2 vs. G1	8	1804	Fixed-effect	1.58 (1.40, 1.79)
G3 vs. G1	8	1542	Random-effects	2.17 (1.77, 2.67)
G3 vs. G2	8	2206	Random-effects	1.41 (1.25, 1.60)
ER− vs. ER+	12	117988	Random-effects	1.32 (1.22, 1.43)
Age < 50 vs. ≥ 50 years	8	27209	Random-effects	1.00 (0.91, 1.11)
Age < 40 vs. ≥ 40 years	3	1103	Fixed-effect	0.99 (0.81, 1.21)
Pre- vs. post-menopausal	4	1990	Random-effects	1.02 (0.93, 1.12)

CI, confidence interval.