the potential correlation with their own and their cotwin’s value of the environmental moderator. Simulation studies showed that this extended univariate model accurately detected moderation and is more powerful than the bivariate model. However, if the covariance between the moderator and the behavioral outcome is moderated, the extended univariate model does not specify the location of the moderation, and the bivariate model provides the correct test. Conversely, in instances where the bivariate model shows no moderation of the covariance between the behavioral outcome and the moderator, the extended univariate model is the more powerful and appropriate model to test for moderation.
