The fitted trajectories for the 6 group models are displayed graphically in . (Coefficients can be found in Supplemental Table 5.) A, B, and C displays the communication, social, and repetitive behavior trajectories, respectively. The communication and social graphs have 4 features of note. First, many children experienced substantial development. Particularly on the communication dimension, most of the trajectories increased steadily over time. Second, there was substantial heterogeneity in the extent of this development; some children improved much more than others. This heterogeneity is especially visible in the social dimension; some groups improved whereas others, particularly the “low” group, were relatively flat. With 1 important exception, groups that were high-functioning (HF) at the start improved more rapidly. Third, the most rapid development occurred before age 6 years, and several of the trajectories tended to flatten out after that. Finally, both the communication and social dimensions have a group, here identified as “bloomers,” that improved especially quickly. These children started with low scores, comparable to those on the LF trajectories, and improved at a rapid pace, ending with scores comparable to those on the HF trajectories.
(A) Modeled communication, (B) social, and (C) repetitive behavior symptom trajectories based on CDER scores by age.
In contrast, the repetitive behavior trajectories remained relatively stable, except for 1 that decreased in severity and 1 that increased. Although there was diversity in the amount of repetitive behavior observed, only ~15% of children seemed to change significantly over time, one-half of these improving and one-half getting worse. In the analyses that follow, we describe the differences in the composition of the trajectory groups and distinguish bloomers from other children with autism.
Composition of Trajectory Groups
contains descriptive statistics on the population, as well as according to subgroup membership. In general, children on the highest trajectories tended to have been born in the most recent cohorts. Trajectory groups did not differ according to gender. The LF trajectory groups were less likely to be white, more likely to be born as a Medi-Cal recipient, and to have younger, foreign-born mothers with fewer years of education. The HF children tended to be born to older, more educated, white mothers, and were less likely to be a Medi-Cal recipient. Children with intellectual disabilities were more likely to be on LF trajectories.
Descriptive Statistics for Sample of Persons With Autism With at Least 4 Valid Evaluations
Relationship Between Trajectories
describes the relationships between trajectory group memberships. Those on the lowest communication trajectory had ~6 times the risk of being on the lowest social trajectory and were extremely unlikely to be on HF social trajectories. Communication bloomers were heavily concentrated among the social bloomers (RR: 2.58) as well as among the medium–high and high groups, which, like the bloomers, show significant improvement over time, and social bloomers are heavily concentrated among the communication bloomers (RR: 2.75). Meanwhile, communication and social bloomers were unlikely to be in the other’s LF group. Similarly, those on LF social and communication trajectories were more likely to exhibit frequent repetitive behaviors, whereas those on HF trajectories were more likely to exhibit fewer or none.
RRs for Trajectory Group Membership
In general, we found that the 3 dimensions were associated with one another, such that children who were HF on 1 dimension were unlikely to be LF on the others. Yet, there is some independence, so that children may develop at a different pace along these 3 dimensions.
Correlates of “Blooming”
We next investigated the factors that distinguish bloomers, who improve rapidly, from the LF children they initially resemble and the HF children they resemble at the end of the observed trajectory. In , we present the adjusted ORs for being in 1 of the 2 lowest or 2 highest social and communication trajectories, relative to being a bloomer. The middle trajectory was excluded from this analysis to provide a cleaner comparison.
ORs and 95% Confidence Intervals From Multinomial Logistic Regression Results Showing Correlates of LF and HF Trajectories Versus Blooming
Beginning with the communication trajectories, we found that children diagnosed later were more likely to be on HF trajectories, and were less likely to be LF, than bloomers. Children with intellectual disabilities were more than twice as likely to be LF than bloomers (OR: 2.15) and very unlikely to be HF. Children with foreign-born mothers were less likely to be HF than bloomers, but there was no significant difference for the LF group. LF children were less likely to be white (OR: 0.69), whereas HF children were more likely to be white (OR: 1.86). However, among nonwhites, Hispanic children had greater odds of being HF and lower odds of being LF. The LF children were likely to have less-educated mothers, and the highest-educated mothers were more likely to have HF children. Finally, there was no significant difference according to gender or being a recipient of Medi-Cal.
The pattern for social bloomers was similar. There was no difference according to gender or being a Medi-Cal recipient, and maternal education did not affect social trajectories. Both HF and LF groups were less likely than bloomers to be diagnosed after age 3 years. Having an intellectual disability was strongly associated with LF trajectories, as was having a foreign-born mother. Finally, children of white mothers were less likely to be LF than bloomers, as were children of Hispanic mothers (relative to nonwhites).