Unidimensionality in the Rasch model: how to detect and interpret

BRENTARI, EUGENIO; Dipartimento Metodi Quantitativi - Università Degli Studi Di Brescia & GOLIA, SILVIA; Dipartimento Metodi Quantitativi - Università Degli Studi Di Brescia
Unidimensionality, that is the items in a questionnaire measure only a single construct, is a fundamental requirement for the Rasch model. The paper deals with the detection of unidimensionality making use of principal components analysis of residuals and item fit statistics. Simulated bi-dimensional data sets are analized in order to find regolarities in the behavoiur of these statistical tools. The results are applied to a real database coming from the satisfaction section of the first...