Longitudinal data: different approaches in the context of item-response theory models

In this paper, some extended Rasch models are analyzed in the presence of longitudinal measurements of a latent variable. Two main approaches, multidimensional and multilevel, are compared: we investigate the different information that can be obtained from the latent variable, and we give advice on the use of the different kinds of models. The multidimensional and multilevel approaches are illustrated with a simulation study and with a longitudinal study on the health-related quality of life in terminal cancer patients.