Biometric models were fit to the raw data using the Mx software system (Neale, Boker, Xie, & Maes, 2003). For ease of interpretation, the Internalizing variable was reversed to be positively correlated with the marital quality scale (with higher scores corresponding to greater Quality). To correct for potential biases in model fitting, the internalizing and marital relationship scales were adjusted for effects of age and gender (McGue & Bouchard, 1984). Each scale was regressed on age, age2, age × gender, and age2 × gender, and the standardized residuals from these regressions were used in subsequent analyses. Because not all participants had both internalizing and relationship data, we used full-information maximum-likelihood with the raw data, a procedure that was also necessary for the moderated biometric models we were using. Fit of the moderation models were judged relative to the fit of a bivariate “no moderation” model in which the six moderation parameters (βXc and βXu for A, C, and E) were fixed at zero (so that aC+βXcM became aC + (0*M) = aC).
