title: Modeling the World Health Organization Disability Assessment Schedule II using non-parametric item response models.
abstract: The World Health Organization Disability Assessment Schedule II (WHO-DAS II) is a multidimensional instrument developed for measuring disability. It comprises six domains (getting around, self-care, getting along with others, life activities and participation in society). The main purpose of this paper is the evaluation of the psychometric properties for each domain of the WHO-DAS II with parametric and non-parametric Item Response Theory (IRT) models. A secondary objective is to assess whether the WHO-DAS II items within each domain form a hierarchy of invariantly ordered severity indicators of disability. A sample of 352 patients with a schizophrenia spectrum disorder is used in this study. The 36 items WHO-DAS II was administered during the consultation. Partial Credit and Mokken scale models are used to study the psychometric properties of the questionnaire. The psychometric properties of the WHO-DAS II scale are satisfactory for all the domains. However, we identify a few items that do not discriminate satisfactorily between different levels of disability and cannot be invariantly ordered in the scale. In conclusion the WHO-DAS II can be used to assess overall disability in patients with schizophrenia, but some domains are too general to assess functionality in these patients because they contain items that are not applicable to this pathology.
authors.affiliation: Department of Epidemiology and Biostatistics, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Francisca
authors.initials: F
authors.lastname: Galindo-Garre
authors.forename: María Dolores
authors.initials: MD
authors.lastname: Hidalgo
authors.forename: Georgina
authors.initials: G
authors.lastname: Guilera
authors.forename: Oscar
authors.initials: O
authors.lastname: Pino
authors.forename: J Emilio
authors.initials: JE
authors.lastname: Rojo
authors.forename: Juana
authors.initials: J
authors.lastname: Gómez-Benito
mesh_terms: D000203:Activities of Daily Living; D000293:Adolescent; D000328:Adult; D039721:Diagnostic and Statistical Manual of Mental Disorders; D006233:Persons with Disabilities; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D011618:Psychotic Disorders / Q000175:diagnosis*; D012559:Schizophrenia / Q000175:diagnosis*; D012648:Self Care; D012919:Social Behavior; D018709:Statistics, Nonparametric; D014944:World Health Organization; D055815:Young Adult
keywords: Mokken scaling; WHO-DAS II; non-parametric IRT