Model fitting
The likelihood ratio test was first compared with the saturated model (ETable 2A Online Data Supplement) and then with the ACE model (ETable 2B, with best likelihood among quantitative genetic models). A statistically non-significant drop in fit (p=0.884) was observed when comparing the AE model against the ACE model, making the AE model the most parsimonious/final model (ETable 2B).