Table 2.

Estimates (SE) of residual variance (σ2), of monozygous and dizygous covariances (σmonozygous2 and σdizygous2, respectively), of monozygous and dizygous correlations (ρmonozygous and ρdizygous, respectively), and of heritability (H) under the AE model on log dense area and log dense area, separately

EstimateAge adjusted for meanMean adjusted for age and covariates*Random effect a function of age
Log dense area
    σ20.63 (0.023)0.60 (0.022)0.43 + 0.015 (age 40)
    σmonozygous20.43 (0.025)0.39 (0.024)0.31 + 0.007 (age 40)
    σdizygous20.16 (0.030)0.13 (0.029)0.09 + 0.004 (age 40)
    ρmonozygous0.67 (0.021)0.66 (0.022)0.73 − 0.005 (age 40)
    ρdizygous0.25 (0.046)0.21 (0.047)0.21 + 0.001 (age 40)
    H0.66 (0.022)0.65 (0.024)0.71 (0.039)
    −2 Log-likelihood668.1585.8531.8
Log nondense area
    σ20.45 (0.017)0.24 (0.0089)0.28 − 0.004 (age 40)
    σmonozygous20.34 (0.018)0.16 (0.0096)0.19 − 0.002 (age 40)
    σdizygous20.15 (0.021)0.05 (0.012)0.06 − 0.001 (age 40)
    ρmonozygous0.76 (0.017)0.67 (0.022)0.67 − 0.0002 (age 40)
    ρdizygous0.34 (0.042)0.21 (0.044)0.23 − 0.002 (age 40)
    H0.75 (0.017)0.66 (0.023)0.67 (0.036)
    −2 Log-likelihood−162.7−1,165.3−1,178.8
  • * Adjusted covariates for mean log dense area were age, height, weight, age at menarche, number of live births, years of oral contraception use, years of hormone replacement therapy use, menopausal status, and population (Australian vs North American). Adjusted covariates for mean log nondense area were age, height, weight, age at menarche, number of live births, age at first birth, pack years of smoking, and population (Australian vs North American).

  • These analyses allowed the random effects variables to vary as a linear function of age (centered on 40 y).