Evaluation of the metric properties of the WHODAS 2.0, WHODAS-S, and RADS in the assessment of disability in Parkinsonian patients

Objectives: Parkinson's disease is the second most prevalent progressive neurodegenerative disease and causes considerable disability in patients. We conducted a cross-sectional analytical study to examine the metric properties of the World Health Organization Disability Assessment Schedule 2.0 (WHODAS-2); the 12-item World Health Organization Disability Assessment Schedule (WHODAS-S) and the Rapid Assessment of Disability Scale (RADS) in assessing disability in Parkinsonian patients. Patients and methods: Patients with cognitive impairment, neurological disorder, or disability due to any condition other than PD were excluded. One hundred sixty-eight consecutive patients were assessed in ON state. The following attributes were evaluated: data quality and acceptability, reliability, and construct (convergent and known-groups) validity. Testretest reliability was analyzed in fifty-six patients. Results: Out of 168 patients, 65.4% were men's, 96 (57.1%) at stage III of Hoehn and Yahr. One hundred fifty-one patients lived independently in the community, 102 lived with their spouses, 108 were retired, and 48 were still working. Cronbach's alpha exceeded the minimum requirement of 0.70 for the three scales. The SEM obtained was, also for the three scales, higher than the 1/2 of the standard deviation value. The validity for known groups showed that all domains were significantly different in both WHODAS-S and RADS. The stability of the scale was evaluated with the test-retest (ICC). The results for the WHODAS-2 <= 0.002; for the WHODAS-S were p <= 0.000]; and for the RADS were p <= 0.000]. Conclusion: The RADS is by far the fastest scale to use. All three scales showed suitable metric properties