The five trajectories resulting from the model fitting process are depicted in Figure 1. Estimated mean growth parameters for each class are provided in Supplementary Table 1. For subsequent analyses, individuals were assigned to the class in which they had the highest posterior probability of membership; Supplementary Table 2 provides mean posterior probabilities of class membership for individuals assigned to each class. Class 1 (N=362, 3.2% of the sample; persistently high [PH]) is characterized by the second-highest initial level of internalizing symptoms, which increases for several years before stabilizing. Class 2 (N=631, 5.7%; low-to-high [LH]) has relatively low initial levels of internalizing symptoms, but these increase beginning at age 7. Class 3 (N=1048, 9.4%; mid-childhood increase [MCI]) exhibits increasing internalizing symptoms until approximately age 8, after which symptoms decrease. Class 4 (N=785, 7.0%; high-to-low [HL]) begins with the highest levels of problems, which decrease through age 9 and stabilize thereafter. Individuals in Class 5 (N=8331, 74.7%; stable low [SL]) exhibit consistently low levels of internalizing symptoms. The SL class was the reference class in subsequent analyses. Relationships between each class and demographic variables are described in Table 4.
