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Table 2 Reproductive risk factors by study groupa

From: Risk factors for breast cancer in postmenopausal Caucasian and Chinese-Canadian women

  Adjusted Mean (Lower and Upper 95% Confidence Limits)     
     P
  Caucasians Chinese born in the West or migrated to the West before 21 Recent Chinese migrants P b P c P d P e
  (N = 413) (N = 216) (N = 421)     
Age at menarche (years)f, g 12.8 (12.6, 13.0) 13.0 (12.7, 13.2) 13.7 (13.6, 13.9) 0.01 0.64 <0.001 <0.001
Age at first live birth (years)f, h 24.3 (23.8, 24.7) 24.9 (24.3, 25.5) 25.5 (25.1, 25.9) 0.002 0.34 <0.001 0.22
Number of live births (%)        
0 14.5 (11.3, 18.5) 8.5 (5.2, 13.8) 4.5 (2.8, 7.2) 0.60 0.14 <0.001 0.19
1 9.9 (7.3, 13.2) 7.7 (4.6, 12.7) 18.0 (14.3, 22.4) 0.08 0.99 0.005 0.007
2 36.9 (32.3, 41.8) 40.1 (33.2, 47.4) 43.3 (38.5, 48.2) 0.14 0.99 0.22 0.99
3 21.6 (17.7, 26.1) 30.8 (24.7, 37.7) 19.6 (15.9, 37.7) 0.08 0.05 0.99 0.008
≥ 4 11.9 (8.9, 15.9) 5.3 (2.9, 9.6) 8.0 (5.7, 11.2) 0.33 0.05 0.24 0.71
Breastfeeding (% yes) 76.6 (71.6, 80.9) 63.4 (55.9, 70.2) 72.1 (66.9, 76.8) <0.001 0.62 <0.001 0.14
Age at natural menopause (years)f, i 50.1 (49.7, 50.6) 50.6 (50.0, 51.3) 49.9 (49.5, 50.3) 0.79 0.53 0.99 0.10
Age at surgical menopause with both ovaries removed (years)f, j 44.0 (41.2, 46.9) 45.0 (41.3, 48.9) 45.0 (42.2, 48.0) 0.68 0.99 0.99 0.99
Ever used oral contraceptives (% yes) 85.8 (81.4, 89.3) 73.9 (67.3, 79.6) 40.7 (35.9, 45.7) <0.001 0.002 <0.001 <0.001
Duration of oral contraceptive use (years)f, k 3.6 (3.0, 4.3) 2.5 (2.0, 3.2) 2.1 (1.7, 2.6) 0.14 0.03 <0.001 0.81
Ever used hormone replacement therapy (% yes) 47.4 (41.7, 53.1) 33.1 (26.6, 40.3) 28.1 (23.9, 32.6) 0.03 0.003 <0.001 0.65
Duration of hormone replacement therapy use (years)f, l 2.1 (1.6, 2.8) 1.7 (1.2, 2.6) 1.1 (0.8, 1.4) 0.01 0.99 0.001 0.17
  1. a P values were based on ANCOVA for continuous variables and logistic regression for binary variables, adjusting for age, education, and age × ethnicity. Pairwise comparisons were adjusted for multiple comparisons using the Bonferroni method. Variables are expressed as adjusted means.
  2. b P values for ethnicity effect.
  3. c P values for comparing Caucasians and Chinese born in the West or migrated to the West before age 21.
  4. d P values for comparing Caucasians and recent Chinese migrants.
  5. e P values for comparing Chinese born in the West or migrated to the West before age 21 and recent Chinese migrants.
  6. f Log transformed.
  7. g There were 3 missing values for Chinese born in the West or migrated to the West before age 21 and 2 missing values for recent Chinese migrants.
  8. h Sample size was 344 Caucasians, 191 Chinese born in the West or migrated to the West before age 21, and 397 recent Chinese migrants.
  9. i Sample size was 274 Caucasians, 159 Chinese born in the West or migrated to the West before age 21, and 345 recent Chinese migrants.
  10. j Sample size was 28 Caucasians, 13 Chinese born in the West or migrated to the West before 21, and 24 recent Chinese migrants.
  11. k Sample size of oral contraceptive uses was 313 Caucasians, 154 Chinese born in the West or migrated to the West before 21, and 169 for recent Chinese migrants.
  12. l Sample size of hormone replacement therapy users was 201 Caucasians, 68 Chinese born in the West or migrated to the West before 21, and 118 recent Chinese migrants.
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