Table 1.

Characteristics of the Norwegian and Swedish Women's Lifestyle and Health Cohort Study and of the incident cases of breast cancer during follow-up until the end of 1999

No. of women53,44846,26999,717
Age (y) at cohort entry, mean (range)40.9 (34-49)39.3 (30-49)40.1
Person-years of follow-up until outcome or censoring360,801311,634672,436
No. of women with invasive breast cancer diagnosed before age 50 (premenopausal)426307733
Age (y) at diagnosis of breast cancer (diagnosed before age 50), mean (range)44.8 (36-50)44.4 (30-50)44.7