Table 1.

Selected characteristics of participants and nonparticipants in the CWLS

Characteristics at diagnosis*CWLS participants (n = 4,482)CWLS nonparticipants (n = 7,786)
Mean age at diagnosis (y)58.559.4
Breast cancer stage at diagnosis (%)
Mean age at menarche (y)12.712.8
Mean age at first live birth (y)24.424.3
Parity, mean2.72.6
Postmenopausal (%)72.772.3
Education, ≥12 y (%)91.482.9
BMI (kg/m2), mean25.626.1
Early-life vigorous-intensity recreational physical activity§ (%)
Smoking history (%)
Alcohol (drinks daily), mean3.33.1
  • * Data obtained in parent case-control studies.

  • Excludes women with missing information on postdiagnosis physical activity (n = 136), distant metastases (n = 35) or unknown (n = 615) stage breast cancer at diagnosis, and any recurrence of breast cancer (n = 535).

  • Excludes women with distant metastases (n = 134) or unknown (n = 898) stage breast cancer at diagnosis, who died before January 1, 1999 (n = 2,663), and who did not receive the CWLS questionnaire (n = 989).

  • § Defined as participation in vigorous-intensity physical activities, such as running; jogging; bicycling, including stationary; calisthenics, aerobics, aerobic dance, and rowing machine; and tennis.