For a plot of the average quartic trajectory of externalizing problems overlaid with the means of externalizing problems over time, see Figure 1. The means of externalizing problems showed decreases from ages 5–11, followed by increases from 11–16, and decreases from 16–27. For a plot of individuals’ quartic trajectories of externalizing problems, see Figure 2. Although the average trajectory is fairly flat, the individual trajectories show considerable variability, both in intercepts, slopes, and curvatures, suggesting that the development of externalizing problems differs between people.
