With reference to the questionnaire adopted within the Italian project
"Ulisse" to assess health condition of elderly people, we investigate two
important issues: discriminant power and actual number of dimensions measured
by the items composing the questionnaire. The adopted statistical approach is
based on the joint use of the latent class model and a multidimensional item
response theory model based on the 2PL parametrization. The latter allows us to
account for the different discriminant power of these items.