Table 1.

Distribution of matching variables, mammographic density and potential confounders by case-control status

CharacteristicCase, nCase, mean (SE) or n (%)Control, nControl, mean (SE) or n (%)
Matching variables
    Age at earliest mammogram37261.3 (10.4)71361.1 (10.0)
    Interval between early and late mammograms3727.1 (1.5)7137.0 (1.5)
    Number of screening mammograms3725.0 (1.4)7135.2 (1.8)
    Residence (% Olmsted County)18349.6%36551.2%
    Postmenopausal at exam date (%)36398.1%70099.2%
Density variables
    Percent density from earliest mammogram
        Ipsilateral side37230.5 (14.0)70826.6 (14.8)
            Age, 40-49 y6340.5 (12.0)11535.5 (14.0)
            Age, 50-59 y10732.2 (14.1)20828.5 (15.2)
            Age, 60-69 y11328.8 (13.0)23323.8 (14.0)
            Age, 70+ y8923.6 (12.2)15221.6 (12.5)
        Contralateral side36830.8 (14.4)71026.6 (14.6)
            Age, 40-49 y6341.8 (13.2)11536.1 (13.7)
            Age, 50-59 y10733.0 (14.1)20828.4 (15.1)
            Age, 60-69 y10927.9 (13.6)23523.3 (13.7)
            Age, 70+ y8923.8 (11.1)15221.9 (12.0)
    Difference in percent density from earliest to latest mammogram
        Ipsilateral side (current PD − first PD)371-1.3 (7.5)707-1.2 (6.3)
        Contralateral side (current PD − first PD)367-1.5 (7.4)709-1.1 (6.5)
Covariates
    BMI (kg/m2) at earliest mammogram35127.6 (5.0)69627.1 (5.1)
    Changes in BMI from earliest mammogram to latest mammogram3500.25 (2.0)6940.46 (2.0)
    First degree family history of breast cancer
        No31484.4%62587.7%
        Yes5815.6%8812.3%
    Menopausal status at earliest mammogram
        Premenopausal5815.7%12417.6%
        Postmenopausal31284.3%58282.4%
    HT use
        Never22059.1%34047.7%
        Yes
            During mammogram interval12433.3%33747.3%
            Not during interval41.1%111.5%
            Unknown time period246.5%253.5%
    AFB and parity combined
        Nulliparous4411.3%9112.8%
        AFB ≤ 20, 1 or 2 children195.1%273.8%
        AFB > 20, 1 or 2 children12232.8%20428.7%
        AFB ≤ 20, 3+ children6016.1%11816.6%
        AFB > 20, 3+ children12734.1%27038.0%
  • Abbreviation: AFB, age at first birth.