Demonstrates the use of Rasch models to assess the dimensionality of an item set across cohorts in longitudinal studies. Presents data from a study on adolescents' deductive reasoning ability showing that the same test items can be measuring qualitatively different latent traits in different subsamples or at different time points. (JPB)

Demonstrates how Rasch models can be used to study differences in item salience within and across time points, and that even if a test does not fulfill assumptions of the Rasch model, it can be used to obtain information on item functioning across participants and over time. Illustrates method using longitudinal data from Baltimore Prevention…