Table 1

Comparison of cases and controls by selected demographic factors and major risk factors for breast cancer, Shanghai Breast Cancer Study, 1996–1998

Cases (n = 1144)Controls (n = 1221)Pa
Demographic factors
 Age (yr)b47 (42, 53)47 (40, 54)0.26
 Education ≥ high school (%)43430.16
Established risk factors
 First-degree relative with breast cancer (%)3.52.40.11
 Ever diagnosed with breast fibroadenoma (%)9.95.2<0.01
 No regular leisure physical activity (%)8174<0.01
 Waist-to-hip ratiob0.81 (0.77–0.84)0.80 (0.76–0.84)<0.01
 Body mass indexb23.2 (21.2–25.5)22.8 (20.8–25.1)0.02
 Age at menarche (yr)b14 (13, 16)15 (13, 16)<0.01
 Postmenopausal (%)30340.01
  Age at menopause (%)b,c49 (47, 51)49 (46, 50)<0.01
 No live births (%)6.84.1<0.01
  Age at first live birth (yr)b,d27 (24, 29)26 (24, 28)<0.01
  • a P derived from t tests (continuous variables) or the χ2 test (categorical variables).

  • b Median (25th, 75th percentile) values are presented.

  • c Among postmenopausal women.

  • d Among parous women.