Table 1.

Baseline characteristics of breast cancer cases and controls, SWHS (1997–2000)

CharacteristicsCases (N = 504)Controls (N = 1,082)Pdifferencea
Age (y, mean ± SD)53.4 ± 9.055.0 ± 9.00.001
Education ≥ high school, %48.861.8<0.001
Postmenopausal, %48.655.70.008
Family history of breast cancer, %4.81.6<0.001
BMI (among postmenopausal women, %)24.9 ± 3.624.8 ± 3.70.618
Regular physical activity, %34.738.10.198
Ever consumed alcohol regularly, %1.82.50.377
Ever smoked cigarette regularly, %1.43.10.050
Age at menarche (y, mean ± SD)14.7 ± 1.715.0 ± 1.70.019
Age at first live birth (y, mean ± SD) among parous women26.4 ± 4.225.4 ± 4.3<0.001
Number of live births (mean ± SD) among parous women1.7 ± 1.02.0 ± 1.2<0.001
Breastfeeding (months, mean ± SD) among parous women13.3 ± 14.918.5 ± 19.6<0.001
Age at menopause (y, mean ± SD) among postmenopausal women49.1 ± 4.849.2 ± 3.90.848
Use of HRT, %2.41.90.749
  • aP values derived from t tests for continuous variables or χ2 tests for categorical variables.