Table 1.

Baseline Characteristics of the Cohort and of Breast Cancer Cases, Multiethnic Cohort Study, 1993–1996 to 2004/2005

Characteristic	Entire Cohort (n = 84,427)	Cases (n = 3,270)	Breast Cancer Incidence Ratea
Mean age at cohort entry, years	59.1 (8.8)b	60.1 (8.5)
Race/ethnicity, %
African-American	18.6	19.1	336.2
Japanese-American	28.1	30.7	418.8
Latina	20.5	14.7	233.7
Native Hawaiian	7.4	8.8	506.4
White	25.5	26.6	359.2
Body mass indexc, %
<25	47.7	45.5	351.2
25–<30	31.0	32.2	347.5
≥30	21.3	22.3	363.0
Age (years) at menarche, %
≤12	49.9	51.9	369.6
13–14	38.2	37.5	348.5
≥15	11.8	10.6	292.0
Age (years) at first livebirth, %
Nulliparous	13.0	15.8	440.3
≤20	28.9	23.1	269.1
21–25	35.1	34.3	342.2
26–30	16.3	18.5	426.5
≥31	6.7	8.3	474.4
Parityd, %
1	13.0	14.5	407.5
2–3	51.3	55.1	368.8
≥4	35.6	30.4	272.1
Type of menopause, %
None (premenopausal)	15.2	13.0	307.9
Natural menopause	53.0	57.0	366.2
Oophorectomy	14.9	13.4	285.1
Hysterectomy	16.9	16.7	341.5
Postmenopausal hormone therapy, %
Never use	52.4	45.4	316.3
Former use	16.8	16.0	299.4
Current use of estrogen therapy	14.1	14.2	329.3
Current use of estrogen-progestin therapy	16.8	24.4	500.6
Alcohol intake (drinks/day), %
0	60.8	59.0	343.8
<2	33.9	33.7	349.7
≥2	5.3	7.3	487.7
First-degree family history of breast cancer, %
No	88.9	82.7	330.2
Yes	11.1	17.3	546.2

^aIncidence rate per 100,000 women; age-adjusted to the 1970 US standard population.

^bNumbers in parentheses, standard deviation.

^cWeight (kg)/height (m)².

^dAmong parous women.