title: Validation of the "World Health Organization Disability Assessment Schedule, WHODAS-2" in patients with chronic diseases.
abstract: BACKGROUND
  The WHODAS-2 is a disability assessment instrument based on the conceptual framework of the International Classification of Functioning, Disability, and Health (ICF). It provides a global measure of disability and 7 domain-specific scores. The aim of this study was to assess WHODAS-2 conceptual model and metric properties in a set of chronic and prevalent clinical conditions accounting for a wide scope of disability in Europe.
  
  
  METHODS
  1,119 patients with one of 13 chronic conditions were recruited in 7 European centres. Participants were clinically evaluated and administered the WHODAS-2 and the SF-36 at baseline, 6 weeks and 3 months of follow-up. The latent structure was explored and confirmed by factor analysis (FA). Reliability was assessed in terms of internal consistency (Cronbach's alpha) and reproducibility (intra-class correlation coefficients, ICC). Construct validity was evaluated by correlating the WHODAS-2 and SF-36 domains, and comparing known groups based on the clinical-severity and work status. Effect size (ES) coefficient was used to assess responsiveness. To assess reproducibility and responsiveness, subsamples of stable (at 6 weeks) and improved (after 3 moths) patients were defined, respectively, according to changes in their clinical-severity.
  
  
  RESULTS
  The satisfactory FA goodness of fit indexes confirmed a second order factor structure with 7 dimensions, and a global score for the WHODAS-2. Cronbach's alpha ranged from 0.77 (self care) to 0.98 (life activities: work or school), and the ICC was lower, but achieved the recommended standard of 0.7 for four domains. Correlations between global WHODAS-2 score and the different domains of the SF-36 ranged from -0.29 to -0.65. Most of the WHODAS-2 scores showed statistically significant differences among clinical-severity groups for all pathologies, and between working patients and those not working due to ill health (p < 0.001). Among the subsample of patients who had improved, responsiveness coefficients were small to moderate (ES = 0.3-0.7), but higher than those of the SF-36.
  
  
  CONCLUSIONS
  The latent structure originally designed by WHODAS-2 developers has been confirmed for the first time, and it has shown good metric properties in clinic and rehabilitation samples. Therefore, considerable support is provided to the WHODAS-2 utilization as an international instrument to measure disability based on the ICF model.
authors.affiliation: Health Services Research Unit, IMIM-Hospital del Mar, Barcelona, Spain.
authors.forename: Olatz
authors.initials: O
authors.lastname: Garin
authors.forename: Jose Luis
authors.initials: JL
authors.lastname: Ayuso-Mateos
authors.forename: Josué
authors.initials: J
authors.lastname: Almansa
authors.forename: Marta
authors.initials: M
authors.lastname: Nieto
authors.forename: Somnath
authors.initials: S
authors.lastname: Chatterji
authors.forename: Gemma
authors.initials: G
authors.lastname: Vilagut
authors.forename: Jordi
authors.initials: J
authors.lastname: Alonso
authors.forename: Alarcos
authors.initials: A
authors.lastname: Cieza
authors.forename: Olga
authors.initials: O
authors.lastname: Svetskova
authors.forename: Helena
authors.initials: H
authors.lastname: Burger
authors.forename: Vittorio
authors.initials: V
authors.lastname: Racca
authors.forename: Carlo
authors.initials: C
authors.lastname: Francescutti
authors.forename: Eduard
authors.initials: E
authors.lastname: Vieta
authors.forename: Nenad
authors.initials: N
authors.lastname: Kostanjsek
authors.forename: Alberto
authors.initials: A
authors.lastname: Raggi
authors.forename: Matilde
authors.initials: M
authors.lastname: Leonardi
authors.forename: Montse
authors.initials: M
authors.lastname: Ferrer
mesh_terms: D000328:Adult; D002908:Chronic Disease; D004185:Disability Evaluation; D005060:Europe; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D011788:Quality of Life; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D012959:Socioeconomic Factors; D014944:World Health Organization