Co-Occurrence of Internalizing Difficulties and Aggression in Early Childhood and Risk of Later Mental Health Problems: The Norwegian Mother, Father and Child Cohort Study

Understanding whether co-occurrent internalizing difficulties (ID) and aggression in early childhood convey increased risk for later mental health problems is important for theoretical and clinical purposes. To investigate this, mothers from the Norwegian Mother, Father and Child Cohort Study (MoBa) reported on child ID and aggression at ages 3 (n=54,644; 26,750 girls) and 5 (n=38,177; 18,794 girls); depressive, anxiety, conduct-related, and opposition-defiant symptoms at age 8. Using ID and aggression, four profiles emerged: low-symptom/normative; primarily internalizing; primarily aggressive; co-occurrent. The “co-occurrent” group exhibited highest levels of depressive, anxiety and opposition-defiant symptoms at 8 years. The heterogeneity between early manifestation of ID and aggression, and specific type of later mental health symptoms supports a shared aetiology between internalizing and externalizing difficulties.