Table 2. Pooled measures on the relation of breastfeeding and EC.
| Heterogeneity | |||||
|---|---|---|---|---|---|
| Subgroup | Number of studies | RR (95%CI) | I2 (%) | P value | Article included |
| All | 15 | 0.74(0.58 to 0.95) | 64.9 | 0.00 | 18–32 |
| Ever/never | 14 | 0.88(0.72 to 1.06) | 64.0 | 0.00 | 18–31 |
| Study region | |||||
| Asia | 5 | 0.57 (0.37 to 0.87) | 47.6 | 0.11 | 23,27,28,30,31 |
| Europe | 4 | 1.00 (0.66 to 1.53) | 63.9 | 0.04 | 19,26,29,32 |
| North America | 5 | 0.82 (0.60 to 1.13) | 56.1 | 0.06 | 18,20,22,24,25, |
| Other | 1 | 0.23 (0.08 to 0.66) | - | - | 21 |
| Study design | |||||
| Cohort study | 3 | 0.62(0.41 to 0.94) | 36.5 | 0.21 | 19,27,28 |
| Case-control study | 12 | 0.78(0.59 to 1.04) | 67.9 | 0.00 | 18,20–26,29–32 |
| Adjustment for hormone use | |||||
| Yes | 5 | 0.63(0.41 to 0.97) | 61.1 | 0.04 | 18,22,25,26,28 |
| No | 9 | 0.77(0.58 to 1.03) | 67.4 | 0.00 | 19–21,23, 24,27,29–31 |
| Adjustment for oral contraceptive use | |||||
| Yes | 5 | 0.72(0.44 to 1.19) | 74.6 | 0.00 | 18,26,28,29,31 |
| No | 9 | 0.71(0.54 to 0.93) | 58.0 | 0.02 | 19–25,27,30 |
| Adjustment for body mass index | |||||
| Yes | 8 | 0.65(0.44 to 0.96) | 74.7 | 0.00 | 19,22,23, 26,28–31 |
| No | 7 | 0.83(0.63 to 1.08) | 41.4 | 0.13 | 18,20,21, 24,25,27 |
| Adjustment for menarche age | |||||
| Yes | 5 | 0.70(0.42 to 1.17) | 76.7 | 0.00 | 20,21,26,28,29 |
| No | 9 | 0.71(0.55 to 0.92) | 51.6 | 0.04 | 18,19,22–25,27,30,31 |
| Adjustment for menopausal status | |||||
| Yes | 5 | 0.65(0.38 to 1.11) | 82.6 | 0.00 | 20,22,23,28,29 |
| No | 9 | 0.76(0.60 to 0.97) | 41.2 | 0.09 | 18,19,21, 24–27,30,31 |