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An investigation of the discriminant power and dimensionality of items used for assessing health condition of elderly people

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. The analysis is based on the data collected on a sample of 1699 elderly people hosted in 37 nursing homes in Italy. This analysis shows that the selected items indeed measure a different number of dimensions of the health status and that they considerably differ in terms of discriminant power (effectiveness in measuring the actual health status). Implications for the assessment of the performance of nursing homes from a policy-maker prospective are discussed.