Table 1.

Selected characteristics of the participants (N = 102,098) in the Norwegian-Swedish Cohort Study, 1991-2000

Age at enrollment, median (range)41 (34-50)40 (30-50)40 (30-50)
Number of women54,32147,777102,098
Person-years of follow-up493,832430,936924,768
Median follow-up time in years9.69.39.3
Number of invasive breast cancers*6935471,240
Crude breast cancer incidence rate140127134
Age-adjusted breast cancer incidence rate131127127
Age at breast cancer diagnosis, median (range)48 (36-57)49 (30-58)48 (30-58)
Smoking status at cohort enrollment§
    Current (%)29.326.628.0
    Past (%)38.832.736.0
    Passive (%)22.924.223.5
    Never (%)9.016.512.5
  • * Incident cases of breast cancer during follow-up through 2000.

  • Number of incident cases per 100,000 woman-years.

  • Per 100,000 woman-years, adjusted to World Standard population.

  • § χ2 test for differences between Sweden and Norway, P < 0.001.

  • Women who never smoked, but lived with smokers during childhood or at cohort enrollment.