For Extraversion (total N = 29,501 pairs), the base model had a χ2 of 97.15. Restricting the opposite-sex twin correlation led to a χ2 of 104.67, a difference of 7.54, which is significant at one degree of freedom. We therefore allowed for qualitative sex difference when testing for quantitative sex differences (equating h m to h f, and d m, to d f,). This restriction led to a χ2 of 101.20, a non-significant change of 4.06 at 2 degrees of freedom, p = 0.13. Thus, there seem to be only qualitative differences in genetic variance components. Dropping non-additive genetic variance from the model resulted in a significantly higher χ2 statistic, of 194.60, a difference of 93.40.
