Hello,
In the video reviewing path analysis, why do we include VE when calculating the covariance in the ADE model? I had thought the covariance for MZ twins would be VA + VD and the covariance for DZ twins would be .5VA +.25VD. But the slide states that the covariance for DZ twins would be “.5VA+.25VD+VE” (around 20:46 in the video).
Thank you!