. Author manuscript; available in PMC: 2015 Apr 1.

Published in final edited form as: Cancer Epidemiol Biomarkers Prev. 2014 Jan 27;23(4):622–628. doi: 10.1158/1055-9965.EPI-13-1043

Table 1.

Distribution of demographic characteristics and known breast cancer risk factors for cases and controls included in the study

Category	Cases (N=3,472)	Controls (N=3,595)	P value
Demographic Factors^a
Age (yr ± SD)	53.2 ± 10.0	53.0 ± 9.3	0.38
Education ≥ high school (%)	55.9	40	< 0.01
Reproductive Risk Factors
Age at menarche (yr)	14.4± 1.7	14.9 ± 1.8	< 0.01
Postmenopausal (%)^b	49.8	53.1	< 0.01
Age at menopause^b	49.0 ± 4.2	48.8 ± 3.9	0.29
Age at first live birth (yr)^c	26.9 ± 3.8	25.6 ± 4.1	< 0.01
Other Risk Factors
First-degree relative with breast cancer (%)	5.3	2.2	< 0.01
Body mass index (BMI)	24.1 ± 3.5	23.9 ± 3.4	0.05
Body mass index (BMI)^b	24.7 ± 3.7	24.4 ± 3.5	0.01

Unless otherwise specified, mean ± sd are presented;

Among postmenopausal women;

Among parous women.