We first fitted general sex-limitation models for each of the variables, allowing for qualitative and quantitative differences in the sources of variation between the sexes. Subsequently, we fitted common effects sex-limitation models, which only allow for quantitative sex differences in the variance components. Comparing the model fit between these models indicated no significant deterioration in fit for any of the traits (all p>0.05), implying no differences in the source of genetic variation between males and females. We then tested for quantitative sex differences by constraining the variance estimates to be equal across sexes. Male and female path estimates could not be equated for conduct disorder (Δχ2(2)=10.04, p=0.007). Therefore, in subsequent modelling we estimated the variance components separately for males and females.
