Hi all, I am running a nuclear twin family design with siblings, and I find a significant contribution of S, the sibling-shared environment. That is because my twin-sib and sib-sib correlations are stronger than my parent-offspring correlations. My question is, can this shared-environment effect also be described as a generational effect? As in, could it due to an overall change of environment that would mean all people from a same generation have a similar increase/decrease in that trait compared to previous generations, or does the shared-environment have to be interpreted as a family-specific thing?