Figure 1 presents a path model of the biometric moderation model used in this study. This model is an extension of the bivariate (Cholesky) decomposition model, which is used to compute the genetic and environmental influences that are shared between two variables. In the moderation model, the variable being moderated (here, internalizing pathology) is the downstream variable in the model. There are two sets of paths contributing genetic and environmental influences: those common to internalizing and the moderator (marital quality), and those unique to internalizing. The paths from the moderator (M) variable to the dependent variable are linear functions of the form a + βM, where a is the parameter for genetic influence on the variable, β is a regression coefficient, and M is the level of the moderator variable. The total phenotypic variance in Internalizing can be calculated by squaring and summing all of the paths leading to it: P2= (aC+βXcM)2 + (aU+βXuM) 2 + (cC+βXcM)2 + (cU+βXuM)2 + (eC+βXcM) 2 + (eU+βXuM) 2.
