implications about environmental causation or lack of it. While the ACE model is effective in using both MZ and DZ twins, it is blind for non-additive genetic effects. That is why we also provide the within- and between-MZ-twin pair logistic regression coefficients. In such an analysis, dependent errors across the twin pairs need to be modelled, for example, using generalized estimating equations [46,48]. We implemented Generalized estimating equations using “geepack” R package, version 1.2–0.1. Since the MZ twins share all their genes, this analysis does take into account also the possible non-additive genetic effects.
