Chapter 11 Two-Occasion Change

In this section we will introduce longitudinal models in their most basic form: repeated measures collected at two occasions.

Two-occasions data are a natural starting point for studying change: all longitudinal data collection begins with two occasions. Given any two-occasion repeated measures data, popular analytic approaches include the ANCOVA (autoregressive) and difference score models.

This script works through some basic representations of change, more specifically (1) autoregressive models of change, and (2) difference-score models of change. These two models consider and answer different kinds of research questions: questions about change in interindividual differences and questions about intraindividual change.