Abstract
Behavior disorders, such as self-injurious, stereotypic, and aggressive behavior are common among individuals with intellectual or developmental disabilities. While we have learned much about those behaviors over the past few decades, longitudinal research that looks at developmental trajectory has been rare. This study was designed to examine the trajectory of these three forms of severe behavior disorders over a one year time period. The behaviors were measured on two dimensions: frequency of occurrence and severity. Participants were 160 infants and toddlers at risk for developmental delays in Lima, Peru. Using structural equation modeling, we found that the frequency of self-injury and stereotypic behavior and the severity of aggressive behavior remained stable over the 12-month period. Uni-directional structural models fit the data best for self-injurious and aggressive behavior (with frequency being a leading indicator of future severity of self-injury and severity being a leading indicator of future frequency for aggression). For stereotypic behavior, a cross-lagged autoregressive model fit the data best, with both dimensions of frequency and severity involved as leading indicators of each other. These models did not vary significantly across diagnostic groups, suggesting that toddlers exhibiting behavior disorders may be assisted with interventions that target the specific frequencies or severities of behaviors, regardless of diagnostic category.