Il parametro di dipendenza e la violazione della proprietà dell'indipendenza stocastica nell'analisi di Rasch

The stochastic independece property demonstrated among the items of a questionnaire by means of the Rasch Simple Logistic Model could be violated when specific similariets are hypothesised among items which belong to subsets of items of the original questionnaire. The Dispersion Location of Items Model (DLIM) and the dispersion parameter which specifies the model allow to demonstrate such violation. in this study an example is made in which the DLIM is applied to the items of the "relation area" of the Family Environment Scale. Three subsets of items have been analysed by means of the DLIM. the dispersion parameter, redenomated dependece parameter, account for dependencies among the items of the subtest "expressiveness". The DLIM demonstrates to be very useful whenever an hypothesis of similarity is made in relation to the items of a subset which belongs to a larger set of items characteristic of a questionnaire.