The similarity of results across diagnostic groups suggested that the profiles of TF activity are similar for these different facets of externalizing psychopathology. Similar TF profiles across groups supports previous findings (e.g. Krueger et al., 2002) of an externalizing factor underlying these disorders. As illustrated in the profile plot of energy amplitudes for each group (Figure 2), all diagnostic groups show comparable TF component profiles, with similarly reduced component amplitudes compared to the control group. To assess statistically whether amplitude of the TF components might be related to externalizing psychopathology, regardless of the specific diagnosis, we fit a common factor model to the (log-transformed) number of symptoms of each disorder. For drug dependence, we took the maximum number of symptoms of any of the eight classes of illicit substances. We included either PC2 or PC3 (given the significant results of the bivariate regression analyses) and allowed the component score to correlate with the common factor representing the shared variance among symptom counts of all disorders. Further, the variance unique to each disorder was allowed to correlate with each component, one
