Figure 4

Meta-analysis of the association between birth order and risk for breast cancer. The tests for homogeneity and for publication bias in the studies analyzed are as follows. Category I (birth order 2+) versus reference (birth order 1): Q = 87.79 (13 degrees of freedom), P < 0.01; Begg test, P = 0.44; Egger test, P = 0.46. Category II (birth order 5+ and 2 to 4) versus reference: Q = 4.56 (6 degrees of freedom), P = 0.60; Begg test, P = 0.37; Egger test, P = 0.44. Category II (birth order ≥6, 2 to 5) versus reference: Q = 14.42 (6 degrees of freedom), P = 0.60; Begg test, P = 0.37; Egger test, P = 0.44. ¹Category I of birth order was 2+ vs 1. ²Category II of birth order was composed of two conditions: 5+ and 2 to 4; and ≥6 and 2 to 5 vs 1. ³We used adjusted odds ratios (ORs) for meta-analysis because the numbers of cases and controls were not represented in the original article. CI, confidence interval.