Third variables in longitudinal research: Application of longitudinal mediation and moderation in school psychology

Third variable models, such as mediation and moderation, can identify contextual factors that help explain the relation between two variables. Although used less frequently in school psychology research, longitudinal mediation, longitudinal moderation, and the integration of these two approaches can be used to describe the developmental changes in children's psychological and behavioral processes throughout the school years and beyond. This article provides conceptual descriptions of longitudinal mediation, longitudinal moderation, longitudinal moderated mediation, and longitudinal mediated moderation and demonstrates the use of these methods with a large sample of elementary students. Extensions of these methods and applied examples from the literature are also discussed. The Mplus syntax from our illustrated examples are provided for those interested in reproducing the analyses.