We expected that we would be able to model individual differences in trajectories across the long span of development based on findings from previous studies examining shorter spans. However, given the span of development covered and the few previous studies covering as much development, we could not be certain that our model would succeed. We also expected that some of the risk factors that have been associated with externalizing problems in prior studies would be associated with the trajectories of externalizing problems in the present study. Because risk factors may account for common variance in externalizing problems, we expected that some of the risk factors would not have unique effects when controlling for other risk factors. However, again studies with such large arrays of predictors over such lengths of development are few, and theoretical models cannot yet yield definitive hypotheses in such a set of variables, so we could not predict which variables would have the strongest links to externalizing behavior trajectories.
