“…Achenbach (1991) described internalizing and externalizing groups of symptoms, respectively, as ''problems of withdrawal, somatic complaints, and anxiety/depression, on the one hand, and delinquent and aggressive behavior, on the other' ' (p. 66). This distinction, first established four decades ago (Achenbach 1966), continues to have significant heuristic value in research concerning the classification (e.g., Acton and Zodda 2005), description (e.g., Staller 2006), etiology (e.g., Oldehinkel et al 2004), comorbidity (e.g., King et al 2004), underlying personality traits (De Clercq et al 2006) and treatment (Weisz et al 2004) of childhood psychopathology.…”