Research 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.