Validation of the "World Health Organization Disability Assessment Schedule, WHODAS-2" in patients with chronic diseases.
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.
Garin
Olatz
O
Health Services Research Unit, IMIM-Hospital del Mar, Barcelona, Spain.
Ayuso-Mateos
Jose Luis
JL
Almansa
Josué
J
Nieto
Marta
M
Chatterji
Somnath
S
Vilagut
Gemma
G
Alonso
Jordi
J
Cieza
Alarcos
A
Svetskova
Olga
O
Burger
Helena
H
Racca
Vittorio
V
Francescutti
Carlo
C
Vieta
Eduard
E
Kostanjsek
Nenad
N
Raggi
Alberto
A
Leonardi
Matilde
M
Ferrer
Montse
M
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