Understanding early aggression: Empirically derived guidance on type, frequency, and severity in infants and toddlers

Aggressive behavior in toddlers is a significant concern for parents and caregivers. Although aggressive behaviors commonly occur during early development, research suggests that early aggression, particularly when frequent, may signal risk for adverse developmental outcomes. Therefore, understanding how specific aggressive behaviors and their frequencies contribute to overall aggression severity warrants attention. In this study, we employed item response theory (IRT) to examine how both the type and frequency of reported aggressive behaviors relate to underlying (latent) aggression severity. Mothers of 4- to 24-month-old infants and toddlers (n = 874) reported the frequency of 10 physically aggressive behaviors using the Child Behavior Record (CBR). Most children displayed some form of aggression, with "pull hair" and "hit or smack" as the most frequently endorsed behaviors, whereas "hurt animals" was the least frequently endorsed behavior. IRT analyses revealed that "push or shove" was the best indicator for distinguishing toddlers with high and low underlying levels of aggression. For most behaviors, scores above the 95th percentile typically corresponded to high-frequency occurrence (most days to many times each day), whereas scores above the 68th percentile corresponded to lower frequency patterns (some days or higher). However, these thresholds varied by behavior type, with some behaviors (e.g., hurting animals) indicating higher severity even at low frequencies. The results of this investigation provide an empirically derived framework for understanding how both the type and frequency of aggressive behaviors relate to overall severity, potentially informing early identification and intervention strategies.