Fitting the Longitudinal Actor-Partner Interdependence Model as a Dynamic Structural Equation Model in Mplus

Though the Actor-Partner Interdependence Model (APIM) has been extended to accommodate longitudinal data in the multilevel modeling (MLM) and structural equation modeling (SEM) frameworks, intensive longitudinal dyadic data with many (20+) timepoints provide technical challenges for researchers that neither framework fully addresses. We provide an overview of the strengths and weaknesses of MLM and SEM for intensive longitudinal APIMs, then discuss how dynamic structural equation models (DSEMs) are a more general form of both methods and can address their weaknesses in longitudinal APIM analyses. We illustrate how to fit a longitudinal APIM as a DSEM in Mplus with three examples from a daily diary study of heterosexual couples. Specifically, we show (1) when the MLM, SEM, and DSEM will produce similar results, (2) how DSEM can address research questions that traditional MLM and SEM cannot accommodate, and (3) how to specify increasingly complex longitudinal APIMs as DSEMs in Mplus.