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Table 2 Age- and study site-stratified RR (95% CI) for breast cancer in China Kadoorie Biobank

From: Development and external validation of a breast cancer absolute risk prediction model in Chinese population

  Cases Cases/PYs RR (95% CI)
(/100,000)
Highest education
 No formal school 339 44.64 1.00 (reference)
 Primary school 570 60.18 1.17 (1.11 to 1.23)
 Middle school 653 84.82 1.37 (1.24 to 1.51)
 High school 505 124.5 1.60 (1.39 to 1.85)
 College/university 220 165.2 1.87 (1.54 to 2.27)
BMI at age < 50 years, kg/m2
 < 18.5 21 98.83 1.00 (reference)
 18.5–23.9 357 126.42 0.95 (0.84 to 1.07)
 24.0–27.9 187 160.42 0.90 (0.71 to 1.14)
 ≥28 43 135.81 0.85 (0.60 to 1.21)
BMI at age ≥ 50 years, kg/m2
 < 18.5 36 41.07 1.00 (reference)
 18.5–23.9 642 66.66 1.25 (1.17 to 1.33)
 24.0–27.9 683 94.59 1.57 (1.38 to 1.78)
 ≥28 318 118.27 1.96 (1.62 to 2.38)
Height, cm
 < 150.2 382 51.58 1.00 (reference)
 150.2–154.1 504 66.66 1.13 (1.09 to 1.18)
 154.2–158.1 596 78.54 1.28 (1.18 to 1.39)
 ≥ 158.2 805 105.96 1.45 (1.28 to 1.65)
No. of first-degree relatives diagnosed with overall cancer
 0 1795 71.63 1.00 (reference)
 1 402 90.71 1.10 (0.99 to 1.23)
 ≥ 2 90 136.09 1.57 (1.27 to 1.95)
No. of live birth
 Nulliparous 45 112.79 1.78 (1.29 to 2.45)
 1 1067 101.84 1.66 (1.40 to 1.96)
 2 719 74.19 1.41 (1.22 to 1.62)
 ≥ 3 456 47.58 1.00 (reference)
Age at menarche, years
 < 12 187 114.7 1.52 (1.31 to 1.76)
 13–14 748 88.12 1.32 (1.20 to 1.46)
 15–16 837 74.27 1.15 (1.09 to 1.21)
 ≥ 17 515 58.77 1.00 (reference)
  1. Abbreviations: BMI body mass index, PY person-year, RRs relative risk, CI confidence interval
  2. Cox model was stratified by age at enrollment in 5-year interval (10 groups) and 10 study sites. All predictors above were included in the final model