Biometric modeling was used to evaluate the genetic and environmental moderation of P300 amplitude by AAU scores. The bivariate models used in this study (Purcell, 2002) examine the association between P300 amplitude and AAU (see Figure 3). The two models (depicted in Figure 3) are nested: the “Endophenotype” model is a structurally reduced version of the “Alcohol Exposure” model that can be created by constraining all 6 of the moderating parameters (e.g. the βX parameters) to 0. In the first model (“Endophenotype”), the genetic and environmental influences that shape P300 amplitude do not change according to how much alcohol an individual consumes. First, the variance that P300 amplitude and AAU share in common was decomposed into proportions attributable to genetic (a21), shared environmental (c21) and nonshared environmental (e21) influences. Then, the residual variance unique to P300 amplitude was decomposed into genetic (a11), shared environmental (c11) and nonshared environmental (e11) influences. The second, more complex model (“Alcohol Exposure”) is similar to the first, simpler model in nearly all regards except that the six A, C, E components shared and unique to
