Role and Methodology of the Longitudinal Approach in Developmental Research: What, Why, and How?

Abstract

In this paper, we discuss what longitudinal research is, why it is necessary, and how to conduct it in real developmental-research context. Longitudinal research can be conducted using various research designs, but their common features are that data are collected from the same subject at multiple time points and analyses focus on change over time and relationships within individuals. Longitudinal approaches with these characteristics are beneficial to developmental research because they enable the researcher to (1) separate the effects of age, cohort, and period, (2) quantify trajectories of intraindividual change and how these differ between individuals, and (3) identify clues to causal relationships (especially temporal order). Taking a longitudinal approach increases the complexity of research design and data-analysis methodology. However, this cost is offset by the potential to broaden and deepen developmental research by generating creative research questions of a different kind from those generated by cross-sectional studies.