So it seems to me that there are two key things one should do if one wants an unbiased use (/estimates) of the ACE model. One is making sure the classical twin design assumptions are met (e.g. variances equal across groups), etc. I am wondering, on top of this, should normality be explicitly tested for as well? I had read that if the assumptions needed in general for a classical twin design (those relating to mean and variance equality) are violated, that then that would then indicate the data is potentially nonnormal. But, if all the assumptions are satisfied, does that necessarily mean that the data are necessarily normal 'enough' for the ACE model? Or should that also be explicitly tested for using some normality test (even if the variables are fisher-z transformed and all other assumptions are met successfully)?
I appreciate it!