Given that we used changing measures of externalizing problems over time, it was necessary to consider whether the measures showed construct validity invariance. Earlier, we described five necessary conditions for construct validity invariance. First, the measures were chosen from subscales that were 1) theoretically- and developmentally-meaningful, and that were 2) derived empirically (Achenbach & Rescorla, 2001) with a similar factor structure across time (Reitz, Deković, & Meijer, 2005). In addition, the externalizing problems in our study showed 3) strong cross-time consistency and 4) strong convergent and discriminant validity over time with respect to internalizing problems. Also, the items showed 5) high internal consistency at each age. Finally, the patterns of trajectories showed construct validity. Consistent with our findings, previous studies have shown decreases in externalizing problems from early childhood to preadolescence (Leve et al., 2005), and we had found the same in the present sample (Keiley et al., 2000). In addition, studies show that rates of mental disorder increase from late childhood to adolescence, consistent with our findings of increasing rates of externalizing problems during the same time frame (D.
