Disentangling the Direction of Associations between Sleep and Temperament in Toddlers.

Objectives/Background: Although much research has investigated the associations between children's sleep and their temperament, the direction of these associations remains unclear, largely due to a lack of longitudinal studies with repeated assessments of both sleep and temperament. Aiming to clarify the temporal precedence of these two constructs, the current study investigated reciprocal associations between toddlers' sleep and temperament with a longitudinal design. Participants: The sample consisted of 82 toddlers (39 girls) assessed twice. Methods: At both 2 (M = 25.23 months; SD = 1.11) and 3 years of age (M = 36.81 months; SD = 0.91), toddlers' sleep duration and quality were assessed using actigraphy and their temperament was reported by their mothers with the Toddler Behavior Assessment Questionnaire. Results: Shorter nighttime sleep duration (ss = - .28, p = .03) and lower sleep efficiency (ss = - .33, p = .01) at 2 years predicted more temperamental proneness to anger at 3 years, while greater temperamental social fear at 2 years was predictive of shorter 24-hour (ss = - .44, p = .02) and nighttime (ss = - .36, p = .04) sleep duration at 3 years. Associations between temperamental activity level and sleep variables were non-significant. Conclusion: The direction of the associations between toddlers' sleep and their temperament may vary according to which dimension of temperament is considered. These findings should encourage practitioners to identify the beginning of the causal chain leading to sleep or temperamental difficulties so as to develop well-tailored intervention plans.