If the emerging view that common forms of psychopathology are best treated as dimensional phenomena which are dichotomized using data-based but conventional thresholds to facilitate treatment decisions is supported, the present findings have important implications for taxonomy. They support an etiologic explanation for the observation that child and adolescent psychopathology is phenotypically organized within the higher-order internalizing and externalizing domains.3, 15 As with adult psychopathology,8 we hypothesize that dimensions of child and adolescent psychopathology within both the internalizing and externalizing domains are highly correlated largely because they share genetic influences. Furthermore, the present findings suggest an etiologic explanation for the well-documented, but largely ignored, robust correlation between the internalizing and externalizing domains of psychopathology.2, 3, 15 That is, the broad construct of “psychopathology” may have a physical reality in the sense that all 11 psychopathology dimensions were found to share some of the same genetic influences, albeit to varying extents.
