title: A unified approach to multi-item reliability.
abstract: The reliability of multi-item scales has received a lot of attention in the psychometric literature, where a myriad of measures like the Cronbach's α or the Spearman-Brown formula have been proposed. Most of these measures, however, are based on very restrictive models that apply only to unidimensional instruments. In this article, we introduce two measures to quantify the reliability of multi-item scales based on a more general model. We show that they capture two different aspects of the reliability problem and satisfy a minimum set of intuitive properties. The relevance and complementary value of the measures is studied and earlier approaches are placed in a broader theoretical framework. Finally, we apply them to investigate the reliability of the Positive and Negative Syndrome Scale, a rating scale for the assessment of the severity of schizophrenia.
authors.affiliation: Center for Statistics, Hasselt University, Diepenbeek, Belgium. ariel.alonso@uhasselt.be
authors.forename: Ariel
authors.initials: A
authors.lastname: Alonso
authors.forename: Annouschka
authors.initials: A
authors.lastname: Laenen
authors.forename: Geert
authors.initials: G
authors.lastname: Molenberghs
authors.forename: Helena
authors.initials: H
authors.lastname: Geys
authors.forename: Tony
authors.initials: T
authors.lastname: Vangeneugden
mesh_terms: D006801:Humans; D015233:Models, Statistical; D012559:Schizophrenia / Q000175:diagnosis; D012720:Severity of Illness Index