Objective: Our objective was to translate and adapt the disability section of the health assessment questionnaire (HAQ) into German (HAQ-G) to suit Swiss-German conditions and to test its metric properties, reliability, and validity.
Methods: We tested 62 consecutive patients with rheumatoid arthritis (RA) attending the outpatient Clinic of the Department of Rheumatology, University Hospital Zurich. All patients fulfilled the American Rheumatism Association 1987 revised criteria for RA. The translation was done by 2 translators aware of the objective of the questionnaire and some questionable items were discussed and resolved in a panel by 4 rheumatologists including one bilingual clinical researcher. Test-retest reliability was assessed with Pearson's correlation coefficient on the scores of 2 questionnaire mailed in a 10-day interval. The internal consistency was assessed with Cronbach's coefficient alpha. To assess the construct validity, we compared the HAQ scores to clinical, laboratory, and radiological variables of disease activity and outcome. To assess criterion validity, we compared physicians' assessment of functional class (observed disability) to the HAQ (referred disability). The content validity was assessed in a multivariate model explaining HAQ scores with a variety of other measurements of disease activity and outcome.
Results: The test-retest reliability was 0.94; the internal consistency was 0.92; the criterion validity was 0.76; and correlations with other disease variables ranged from 0.39 (Larsen radiological score) to 0.66 (grip strength).
Conclusion: The HAQ-G is a reliable and valid instrument for measuring functional disability in a German speaking population with RA.