Externalizing behavior problems do not emerge suddenly. A high degree of age-to-age stability in externalizing problems appears to be the rule (Fergusson, 1998; Olweus, 1979). Therefore, developmental psychopathology research often describes trajectories of externalizing problems across development. However, to do so across major developmental eras, one must deal with changes in how externalizing behavior is manifested from childhood to adolescence (Olson et al., 2013). For example, young children exhibit more physical aggression (e.g., biting, kicking) and adolescents engage in different forms of externalizing (e.g., drug use, delinquency, indirect aggression; Achenbach, Howell, McConaughy, & Stanger, 1995; Miller, Vaillancourt, & Boyle, 2009). A particular scale may not actually measure the same construct at different ages (Widaman, Ferrer, & Conger, 2010). Thus, changes in measurement may need to accompany changes in externalizing behavior in order for the measures to remain developmentally relevant. The different externalizing behavior manifestations over time do show heterotypic continuity or coherence (for excellent discussions of coherence, see Caspi, 1998; Miller et al., 2009).
