Infant risk factors associated with internalizing, externalizing, and co-occurring behavior problems in young children.

The purpose of the current study was to examine the unique and interactive contributions of infant negative emotionality and family risk factors in the development of internalizing-only, externalizing-only, and co-occurring behavior problems in early childhood. The sample included 412 infants and their primary caregivers. Interviews and temperament assessments took place when infants were 5-7 months old, and primary caregivers completed child behavior ratings at ages 2 1/2 and 5 years. Mixed-effects multinomial logistic regression was used to examine associations between infant risk factors and "pure" and co-occurring child behavior problems, and test whether these associations changed over time. The results of this study showed that hostile parenting during infancy increased the likelihood that children would develop internalizing-only problems, whereas infants who were highly distressed in response to novelty were at increased risk of developing externalizing-only problems. Multiple risk factors, including maternal anxious and depressive symptoms, family conflict, and younger maternal age, independently predicted early childhood co-occurring problems. Additionally, there was a significant interaction between infant anger/frustration and hostile parenting: In the context of hostile parenting, infants high in anger were at increased risk of developing early co-occurring problems, though this association faded by age 5. These findings point to the importance of considering the infant's family context, and differentiating between "pure" and co-occurring behaviors when examining the etiology of early childhood behavior problems.