I'm trying to estimate a twin model that has two groups, but I need to estimate the effect of a covariate on y1 and y2. Specifically, I'm trying to estimate example 5.18 in the new user's manual. I'm trying to augment this model so that it is a MACE model. When I just add the covariate on y1 and y2, I can't seem to identify the model. That is, the model will not converge with a chi-square. Any thoughts as to why and how I can identify my model?
For CFA (perhaps also multiple group CFA), and when using a sample of twins, both MZs and DZs, is it possible to use the stratification option along with type = complex to handle nonindependence of twins in sample?
The CLUSTER option deals with non-independence of observations not STRATIFICATION. Non-independence of twins is already handled in ACE twin models because the two twins are analyzed together in a multivariate model that models the non-independence.
Thanks Linda. I haven't considered the ACE approach because I've not seen examples with twin data using latent variables, especially more than two LVs. In my case I am also doing longitudinal CFA and SEM.