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"When to Worry" about Early Irritability: Developmental Trajectories of Irritability at the Transition to Toddlerhood

Thu, March 23, 11:00 to 11:45am, Salt Palace Convention Center, Floor: 1, Meeting Room 150 B-C

Abstract

Background: Preschool-age irritability is a transdiagnostic marker of internalizing and externalizing problems. However, researchers have generally been reluctant to examine irritability within a clinically salient framework at younger ages due to some instability during the “terrible twos” period. Developmentally sensitive and dense measurements to capture intra- and inter-individual variability, as well as exploration of developmental processes that predict change, are needed. This study aimed to examine (1) the trajectory of irritability at the transition to toddlerhood (12-24 months of age) using intensive longitudinal measures, (2) whether effortful control was associated with individual differences in level and growth rate of irritability, and (3) whether individual differences in the irritability trajectory were associated with later psychopathology.

Method: Data from the When-to-Worry Study were used. Families were recruited when the child was 12-18 months old. Mothers reported on their toddler’s irritability at baseline and every two months until a follow-up laboratory assessment approximately one year later (N = 333). Item Response Theory (IRT) scores from the Multidimensional Assessment Profiles, Infant-Toddler Version were used. About 80% of mothers completed 4 or more irritability assessments longitudinally, and 30% completed 7 or more. Effortful control was measured using Early Childhood Behavior Questionnaire -Very Short Form at baseline. Clinical internalizing/externalizing symptoms were measured using the Preschool Age Psychiatric Assessment at the follow-up assessment (Mean age = 27.77 months). Pairwise correlations of irritability across 12-24 months and intraclass correlation (ICC) were examined. Mixed-effects models were used, controlling for child sex and family income-to-needs ratio in the second and third research questions.

Results: A random intercept and slope of linear time was used. There was an increase in irritability over time (monthly growth rate β=0.03, p < 0.001), yet there was relatively little within-person variability. Pairwise correlations ranged from 0.5 to 0.9 and were highly significant. The ICC was 0.73, suggesting that irritability varied substantially between children, but there was less variation within a child. Effortful control was only associated with the level of irritability (β = -0.24, p < 0.001) and not growth rate. Level of irritability was associated with internalizing (β = 0.50, p < 0.001), externalizing (β = 0.55, p < 0.001), and combined symptoms (β = 0.53, p < 0.001), but growth rate was not.

Conclusions/Implications: The increase in irritability may represent normative developmental increases in autonomy, goal-directed behavior, motor behavior, and parental expectations. The intraindividual stability suggests that screening for elevated irritability at toddler age is meaningful. Earlier prevention, with components involving effortful control, may reduce psychopathology risk later in life. Our findings point to a healthier, earlier approach that can enable detection of transdiagnostic psychopathology risk as early as the child’s first birthday. The long-term objective of this research is to link developmental science discovery to real-world application, enabling earlier identification and ultimately prevention as early as possible to capitalize on the neurodevelopmental malleability in the first years of life.

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