Psychometric properties of world health organization disability assessment schedule 2.0 (WHODAS 2.0) disability scores in Turkish psychiatry patients

Objective: The present study aimed to investigate psychometric properties of a series of disability scores obtained from Turkish version of the WHODAS 2.0 clinician-, self- or proxy-rated forms consisting of either 36 or 12 items. Methods: Following the translation study, 35 psychiatry patients and 35 healthy controls ranging in age between 19 and 65 years self-rated their functional impairment on WHODAS self-report forms. In addition each participant was rated by a relative and by one or two clinicians on WHODAS proxy and rater forms, respectively. There was no significant difference between clinical and control samples in terms of age, sex and aducational attainment. In order to collect evidence for validity and reliability of WHODAS general disability and domain scores, we employed a series of Student's t test to compare scores of the clinical sample with those of the control sample, ROC analyses to determine sensitivity, specifity and accuracy of the scores with an optimal cut-off in differentiating the patients from healthy controls, logistic regression analyses to compute the diagnostic odds ratios of the test, intraclass correlation analyses to estimate agreement among corresponding disability scores obtained from clinician-, self- and proxy-rated forms, Pearson's correlation analyses to gauge agreement between general disability scores obtained from long and short forms, Cronbach alpha and item-total statistics to evaluate internal consistency of the test, and intraclass correlation analyses to investigate the level of agreemet between the clinicians rating identical patients. Findings: Validity and reliability coefficients computed for general disability scores obtained from all three kinds (clinician, self, proxy) of 36-item WHODAS forms were satisfactory or high. In contrast, general disability scores obtained from 12-item short forms were associated with sufficient validity and reliability coefficient only when ratings had been performed by a clinician for clinical subjects. Domain disability scores obtained from long forms were generally associated with adequate or questionable coefficients in clinical sample, but with unacceptable coefficients in the control sample. Conclusion: WHODAS clinician-, patient-, and proxy-rated forms consisting of 36 items, prove to be suitable instruments to assess general disability in Turkish psychiatric patients as well as healthy subjects. Conversely, only one of the three 12-item WHODAS Turkish forms, the clinician-rated form emerges as an instrument with comparable accuracy and precision for measuring general disability in psychiatric patients. We recommend that domain disability scores and short form general disability scores be used to assess samples drawn from clinical populations but not from general population.