Table 3.

Predictors of mammographic density in a multilevel nonlinear growth model

VariableInitial status (age, 32 y)
Rate of change (per decade)
Age (linear)−5.632.500.02
Age2 (nonlinear)1.640.44<0.0001
Case status
    Control (reference)0.000.00
    Caucasian (reference)0.000.00
BMI (kg/m2)
    22.5-24 (reference)0.000.00
Age at menarche (y)
    >14 (reference)0.000.00
Age at first live birth (y)
    None (reference)0.000.00
    0-1 (reference)0.000.00
Menopausal status−1.183.660.75−1.251.650.45
    None (reference)0.00
    Estrogen only1.570.720.03
    Estrogen and progestin3.280.76<0.0001
Soy intake§
  • NOTE: Age, age2 (the square of age), menopausal status, BMI, and HRT are time-varying variables (level 1). All other variables were measured only once at entry into the cohort (level 2).

  • * Estimate is the regression coefficient.

  • Menopausal status was coded 0 for premenopausal, 0.5 for perimenopausal, and 1 for postmenopausal.

  • Hormone replacement use cannot be estimated before menopause.

  • § There is no reference group for soy intake because it is not dummy coded (“as child” and “as adult” can both equal 1).