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| Number of studies | RR (95% CI), fixed effects | RR (95% CI), random effects | |
| Breast cancer | |||
| All studies | 7 | 1.4 (1.3–1.6) | 1.5 (1.2–1.8) |
| Cohort studies | 2 | 1.4 (1.1–1.8) | 1.4 (1.1–1.8) |
| Case-control studies | 5 | 1.4 (1.2–1.7) | 1.5 (1.1–2.0) |
| Europe | 3 | 1.6 (1.3–1.8) | 1.6 (1.2–2.2) |
| North America | 4 | 1.3 (1.1–1.6) | 1.4 (1.1–1.8) |
(Reprinted with the kind permission of Springer Science + Business Media); RR, relative risk; CI, confidence interval
