Internal statistical validation of a quality of life questionnaire

In this paper we present two different statistical approaches to evaluate t he psychometric properties of a quality of life questionnaire, First the st udy of the factorial structure is briefly exposed. Then we present the unid imensional classical models. They are based on the linear relationship betw een the observed score and the true score. The definition of the reliabilit y was first addressed in this classical framework. Its estimation with the Cronbach alpha coefficient is one important feature of the evaluation of an instrument. More recently, modem response theory gives a better statistica l framework to deal with unidimensional latent traits, These models describ e the probability of positive answer to an item as a function of the actual value of the latent trait and an item parameter, We expose the principles of the Rasch model: hypothesis, estimations methods and fit tests, Finally practical applications to the validation process of a questionnaire are exp lored with data from a study of a short French version of the SIP questionn aire.