Change in the magnitude of both un-standardized and standardized variance components as a function of age at 1st drink are shown in Figures 2 and 3 for women and men, respectively. In women and men, change in the total variance (shown by the light solid line) in AD symptoms followed a U-shaped distribution with decreasing variance until age 14 followed by an increase in variance. However, variance in AD symptoms in those with an early age at 1st drink was largely explained by heritable factors whereas the variance in AD symptoms in those who had their 1st drink later in life, particularly after age 18, was largely attributable to unique environmental factors (and/or measurement error). The reduction in the relative magnitude of genetic factors as age at 1st drink increases is shown by the heavy solid line. The corresponding increase in non-shared environmental influences with increasing age at 1st drink is represented by the dotted line. The heavy solid line (representing genetic factors) and the dotted line (representing non-shared environment) intersect, in both men and women, at 13–14 years suggesting differences in the architecture of AD symptoms in those with ages at 1st drink prior and subsequent to this cut-off.
