| Subgroup | OR | 95% CI | p value | No. of studies | Heterogeneity | ||||
| Q-value | P for Q test | I-squared | Tau squared | ||||||
| <20 yr | 0.66 | 0.48 | 0.90 | 0.009 | 3 | 5.88 | 0.053 | 66.0 | 0.05 |
| >20 yr | 0.68 | 0.47 | 0.99 | 0.042 | 3 | 18.61 | 0.001 | 89.3 | 0.09 |
| ER−/PR− | 0.97 | 0.80 | 1.17 | 0.754 | 4 | 5.61 | 0.132 | 46.5 | 0.02 |
| ER+/PR− | 0.82 | 0.67 | 0.99 | 0.043 | 4 | 3.78 | 0.287 | 20.6 | 0.01 |
| ER+/PR+ | 0.80 | 0.68 | 0.93 | 0.003 | 4 | 10.23 | 0.017 | 70.7 | 0.02 |
| Ductal | 0.84 | 0.70 | 1.01 | 0.060 | 5 | 23.14 | 0.001 | 82.7 | 0.03 |
| Lobular | 0.79 | 0.70 | 0.90 | 0.001 | 5 | 0.99 | 0.912 | 0 | 0 |