ABSTRACT
Longitudinal research has substantially increased in the applied psychology area because it could provide more valid evidence than cross-sectional studies. Longitudinal data facilitate describing and understanding growth and developmental processes as well as causal relations between variables over time. Several well-informed decisions need to be made before collecting longitudinal data. These decisions should be based on theoretical considerations, for instance, when and why causal change processes occur; on methodological considerations, for instance, when and how frequently variables should be measured; and on analytical considerations, for instance, what kind of measures (trait vs. state measures) should be used and which statistical method is best suited for analyzing them (e.g., hierarchical linear modelling, cross-lagged panel analysis, growth curve modelling). This chapter provides theoretical, methodological and analytical advice for making these important decisions. First, we provide a general overview of several popular longitudinal research designs in applied psychology (experimental studies, diary studies, and panel studies). Second, we introduce some guidelines for longitudinal data collection including theoretical, methodological and analytical aspects. Third, we summarize the essential considerations one should take into account before collecting longitudinal data.
