[Reliability and validition of the Slovak modified version of the Stanford Health Assessment Questionnaire using the functional disability index in patients with rheumatoid arthritis]

Abstract

Background: Functional disability is one of the most important consequences of RA in the patient's daily life. The HAQ has been widely used in its self administered form for the assessment of disability. A sensitive and valid instrument is needed for a Slovak population with RA.

Objective: To evaluate reliability and validity of the Slovak version of the HAQ in patients with RA and to explore relationships between HAQ score and disease activity and to provide information concerning utilization of this instrument in clinical practice.

Methods: In preparing the Slovak version of the HAQ careful attention has been paid to the translation, in terms of linguistic and conceptual equivalence, in order to preserve the original purpose of the instrument. The wording of some items required adaptation to the current activities of daily living and Slovak lifestyle. The sample consisted of 160 RA-patients, out of which 135 were women and 25 were men. The inclusion criteria were the following: age from 20 to 70 years at the onset of the study, diagnosis of RA according to the ARA criteria. The exclusion criteria were the presence of another serious disease or very disabling RA (stage IV of the Steinbrocker's classification). To analyze the data t-test, correlations, one-way analysis of variance (ANOVA), and principal component analysis (PCA) available in the SPSS/PC+ statistical package were used.

Results: The Cronbach's coefficient of reliability alpha for the HAQ total scale was 0.94. The results of PCA showed that the 20 HAQ items loaded on four components for which the eigen values were greater than 1, accounting for 70% of overall interpersonal variability. Orthogonal varimax rotation of the principal components provided factor loadings reflecting the eight dimensions within the HAQ. Validity of the HAQ was examined further by means of known-groups technique. The HAQ was found to be sensitive to differentiate between the Steinbrocker's functional capacity groups, as well as between males and females. Moreover, significant correlations (p < or = 0.01) were found between the HAQ and the C-reactive protein, the ESR, the NHP-pain, the Ritchie articular index, the Steinbrocker's functional capacity (r = 0.31-0.62) and disease duration (p < or = 0.05, r = 0.17).

Conclusion: The results of the current investigation provide support for reliability and construct validity of the Slovak version of the HAQ in patients with RA. The HAQ has sufficient discriminant ability. The index disability can be used as an criterion of severity of RA, as a criterion of effectiveness in therapeutical trials for patient stratification of the Slovak population with RA.