First, monozygotic and dizygotic polychoric correlations with corresponding asymptotic weights were estimated in Mplus 5.21 for the monozygotic and same-sex dizygotic twin pair data (41). The robust weighted least squares mean and variance estimator was used. Under this method, all twin correlations for all disorder variables are estimated pairwise using all available ordinal raw data for each combination of variables. The weights are the estimated variances of these correlation parameters. These were obtained in Mplus using the TECH3 output and save data options. These asymptotic variances up- or down-weight the contribution of each of the respective polychoric correlations.
