Summary risk estimates of the association between menarcheal age and colorectal cancer risk.

RR: relative risk; CI: confidence interval; CRC: colorectal cancer; OC: oral contraceptive.*P value for heterogeneity within each subgroup.**P value for heterogeneity between subgroups with meta-regression analysis.相对危险度（relative risk, RR）；置信区间（confidence interval, CI）；结直肠癌（colorectal cancer, CRC）；口服避孕药（oral contraceptive, OC）。* 各亚组内异质性的P值。** 采用Meta回归分析得到的亚组间异质性P值。