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[Adaptation of health-related quality of life ("SF-36") questionnaire, its validation and assessment of performance for control group and patients with rheumatoid arthritis].

OBJECTIVE
To adapt the Lithuanian "SF-36" questionnaire, to assess psychometric and life quality criteria for patients with rheumatoid arthritis and for control group.


MATERIAL AND METHODS
Linguistic and cross-cultural adaptation of the Lithuanian "SF-36" questionnaire was made on the basis of the stages referred to in the international project of health quality assessment. For the evaluation of psychometric criteria, data from Vilnius rheumatoid arthritis register (502 patients) and those of the control group (83 people) were used. The reliability of "SF-36" questionnaire was assessed by determining homogeneity, internal consistency of scales and scale stability in time and by calculating the intraclass correlation coefficient. Face, contents and construct validity of the "SF-36" questionnaire has been evaluated, as well as the quality of life of patients with rheumatoid arthritis and those of the control group.


RESULTS
After making linguistic and cultural adaptation of the questionnaire, its final version has been prepared. In assessing the homogeneity of "SF-36", a high and middle-sized correlation between different items of the questionnaire has been noticed in the control group (r=0.51-0.71) and in patients with rheumatoid arthritis (r=0.57-0.83). Internal consistency for the items was also good enough (Kronbach alpha=0.79-0.85) for both tested groups. Stability in time was high for all items of the questionnaire, for the exception of vitality (r=0.074). Face and contents validity of the questionnaire is rather good. Estimates of the correlation between items of the quality of life questionnaire and other questionnaires have shown good convergent and discriminant construct validity. Evaluations of the quality of life in almost all spheres, except emotional, by patients with rheumatoid arthritis were worse than by the rest.


CONCLUSIONS
Questions of health-related quality of life questionnaire are easy to understand and acceptable for the respondents. Reliability and validity of the questionnaire is rather high. For the exception of emotional status, quality of life in almost all spheres was considered as bad by patients with rheumatoid arthritis. The control group had more complaints about the emotional status.