Table 1.

Comparisons of cases and controls on demographics and selected breast cancer risk factors (Shanghai Breast Cancer Study, 1996–1999)

Characteristics	Cases (n = 1,459)	Controls (n = 1,556)	P
Age	47.93 ± 7.99	47.25 ± 8.79	0.24
Education(%)
No formal education	3.63	5.46
Elementary school	8.50	8.42
Middle + high school	74.3	75.4
Profession, college and above	13.6	10.7	0.012
Breast cancer in first-degree relatives (%)	3.7	2.4	0.045
Ever had breast fibroadenoma (%)	9.6	5.0	<0.001
Nulliparous (%)	5.1	3.9	0.126
Age at first live birth (y)	26.7 ± 4.2	26.2 ± 3.9	<0.01
Menarcheal age (y)	14.5 ± 1.6	14.7 ± 1.7	<0.01
Postmenopausal (%)	34.5	36.2	0.321
Menopausal age (y)*	48.1 ± 4.6	47.4 ± 4.9	0.02

^*Among postmenopausal women only.