Table 1 Demographic characteristics and known breast cancer risk factors of study participants^a

 Age (year)

51.6 ± 7.5

51.4 ± 7.3

0.49^b

 Age at menarche (year)

13.0 ± 1.5

12.9 ± 1.4

0.05^b

 Age at menopause (year)^d

49.4 ± 4.5

49.3 ± 4.4

0.54^b

 Number of live births^e

2.9 ± 1.3

3.2 ± 1.5

<0.01^b

 Age at first live birth (year)^e

26.4 ± 5.0

27.5 ± 4.9

<0.01^b

 First-degree relatives with breast cancer (%)

13.2

11.0

0.08^c

 First- or second-degree relatives with breast cancer (%)

19.6

17.8

0.23^c

 Oral contraceptive (%)^f

28.2

31.5

0.06^c

 Hormone replacement therapy (%)^f

9.5

9.8

0.80^c