Table 1.

Descriptive characteristics (means ±SD; percent distribution) of the study sample

VariableAll women (n = 1,893)Menopausal status at time of mammography
Premenopausal (n = 451)Postmenopausal (n = 1,442)
Mammographic breast density (10th, 90th percentile)22.8 ± 14.7 (5.1, 42.5)31.3 ± 15.3 (12.4, 50.9)20.2 ± 13.5 (4.3, 39.4)
Age at mammogram (y)60.4 ± 11.147.7 ± 4.664.4 ± 9.4
Weight at follow-up 1 (lbs)157.3 ± 35.5157.9 ± 35.9157.2 ± 31.4
Age at menarche (y)12.9 ± 1.512.7 ± 1.512.9 ± 1.6
Birthweight (kg)3.35 ± 0.733.31 ± 0.603.36 ± 0.78
    Missing birthweight47%28%53%
Relationship to proband
    Blood relative61%67%59%
    Marry-in39%33%41%
Some college or college graduate47%60%43%
Number of live births, age at first live birth
    Nulliparous9%12%7%
    1-2, ≤20 y6%9%5%
    1-2, >20 y23%34%20%
    3+, ≤20 y22%17%24%
    3+, >20 y33%22%36%
    Missing7%6%7%
Oral contraceptive use
    Never44%12%54%
    Former55%84%46%
    Current1%4%<1%
    Missing<1%0%<1%
Hormone therapy use at follow-up 1
    Never53%80%44%
    Former17%11%19%
    Current30%9%37%
    Missing<1%<1%<1%
Alcohol use at follow-up 1
    Never14%8%16%
    Monthly63%64%62%
    Weekly or Daily23%28%21%
    Missing<1%<1%<1%
Smoking status at follow-up 1
    Never56%52%57%
    Former29%28%30%
    Current15%20%14%
    Missing<1%0%<1%