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Table 1 Baseline characteristics of women by residence and dataset in China Kadoorie Biobank (CKB) and Shanghai Women’s Health Study (SWHS)

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

  CKB SWHS
Rural Urban Urban
Derivation Validation Derivation Validation
No. of participants, n 111,346 55,612 89,204 44,662 73,203
Cases, n 529 267 1007 484 1409
Age in years, mean (SD) and %
 Continuous, years 50.5 (10.2) 50.5 (10.2) 52.6 (10.7) 52.6 (10.7) 52.5 (9.1)
 30- 2.4 2.4 1.7 1.5 --
 35- 15.8 15.7 11.6 11.4 --
 40- 18.3 18.4 15.9 16.1 28.3
 45- 13.2 13.2 14.2 14.6 20.8
 50- 17.6 17.5 17.1 17.4 14.1
 55- 13.6 13.6 13.5 13.4 11.1
 60- 8.9 9.0 9.7 9.3 12.8
 65- 6.1 5.9 9.1 9.2 13.3
 70- 3.7 3.8 6.4 6.4 0.6
 75- 0.4 0.4 0.8 0.8 --
Highest education, %
 No formal school 31.9 31.5 17.3 17.1 10.6
 Primary school 40.3 40.5 20.4 20.0 10.8
 Middle school 21.6 21.6 29.9 30.4 37.2
 High school 5.6 5.8 23.2 23.3 28.0
 College/university 0.6 0.6 9.2 9.1 13.5
Ever smoker, % 5.6 5.5 4.4 4.6 2.8
Ever weekly drinker, % 3.2 3.2 2.6 2.6 2.3
BMI, mean (SD) and %
 Continuous, kg/m2 23.5 (3.4) 23.5 (3.4) 24.2 (3.5) 24.3 (3.5) 24.0 (3.4)
 < 18.5 5.2 5.1 3.2 3.0 3.4
 18.5–23.9 53.8 53.4 46.6 46.5 49.9
 24.0–27.9 31.2 31.6 36.1 36.3 34.6
 ≥ 28 9.9 9.9 14.0 14.2 12.2
Height, mean (SD) and %
 Continuous, cm 153.2 (5.9) 153.2 (5.9) 155.3 (5.9) 155.3 (5.9) 157.5 (5.5)
 < 150.2 29.4 29.4 19.3 19.1 10.3
 150.2–154.1 26.3 26.1 23.6 23.5 17.6
 154.2–158.1 24.1 24.3 26.1 26.1 27.9
 ≥ 158.2 20.2 20.1 31.0 31.3 44.2
No. of affected first-degree relatives, %
 0 85.2 85.5 80.6 80.4 74.7
 1 13.0 12.7 16.8 16.9 21.5
 ≥2 1.8 1.9 2.6 2.7 3.8
Postmenopausal, % 50.2 50.2 55.0 55.3 49.2
No. of live birth, mean (SD) and %
 Continuous 2.5 (1.4) 2.5 (1.4) 1.9 (1.2) 1.9 (1.2) 1.8 (1.2)
 Nulliparous 0.8 0.9 1.9 1.9 3.3
 1 21.1 21.3 50.8 51.2 54.9
 2 38.6 38.2 23.6 23.2 21.1
 ≥ 3 39.4 39.6 23.7 23.7 20.8
Age at menarche, mean (SD) and %
 Continuous, years 15.6 (1.9) 15.5 (1.9) 15.3 (2.0) 15.3 (2.0) 14.9 (1.7)
 < 12 4.7 4.7 6.4 6.4 6.3
 13–14 26.3 26.4 30.3 30.3 36.5
 15–16 38.3 38.4 36.1 36.1 39.5
 ≥ 17 30.6 30.5 27.2 27.3 17.8
Total months of breastfeeding, mean (SD) and %
 Continuous, months 42.4 (32.2) 42.5 (32.4) 24.0 (22.8) 23.9 (22.5) 15.5 (18.3)
 0 2.2 2.4 6.3 6.3 20.2
 1–23.9 36.5 36.5 64.1 64.1 56.6
 24–35.9 17.4 17.2 12.1 12.1 9.9
 36–47.9 14.2 14.0 7.0 7.1 5.9
 ≥ 48 29.6 29.9 10.4 10.3 7.4
Pill use, %
 Never 91.2 91.4 88.7 88.8 78.6
 Ever 8.8 8.6 11.3 11.2 20.4
  1. Abbreviations: SD standard deviation, MET metabolic equivalent of task, BMI body mass index