This tested the hypothesis that genetic components of the six anxiety disorders and MDD load on a higher-order internalizing factor and genetic components of the four disruptive behavior disorders load on a higher-order externalizing factor. Model 3 fit significantly better than Model 2 (Table 3), consistent with the hypothesis5 that at least some genetic factors nonspecifically influence risk for psychopathology dimensions within each of the internalizing and externalizing domains. Based on the results of an earlier phenotypic CFA of the present sample,3 we tested an untabled submodel of Model 3 in which MDD and GAD were allowed to load on both the higher-order internalizing and externalizing genetic factors, but the fit (BIC = 5347) did not improve over Model 3 (Δχ2 = 2.9, DF = 2, P = .23).
