Table 1. Descriptive statistics of the risk factors.

Variable	n=44 690
Age at entry (mean±s.d.)	48.51 (±5.61)
Menstruation length (years) (mean±s.d.)	32.37 (±6.65)
Number of live births
Nulliparous	6537 (14.63%)
≥1	38 153 (85.37%)
Families with breast cancer score (mean±s.d.)	7.17 (±11.30)
Ever have/had other types of breast disease
Yes	7153 (16.01%)
No	37 537 (83.99%)