Translation, cultural adaptation assessment, and both validity and reliability testing of the Kidney Disease Quality of Life - Short Form version 1.3 for use with Iranian patients

Aim: The aims of the study were to translate the Kidney Disease Quality of Life - Short Form version 1.3 (KDQOL-SF ver. 1.3) questionnaire into Iranian (Farsi), and to then assess it in terms of validity and reliability on Iranian patients. Methods: The questionnaire was first translated into Farsi by two independent translators, and then subsequently translated back into English. After translation disparities had been reconciled, the final Iranian questionnaire was tested. An initial test-retest reliability evaluation was performed over a 10 day period on a sample of 20 patients recruited from a larger group (212 patients with end-stage renal disease on haemodialysis). Afterwards, reliability was estimated by internal consistency, and validity was assessed using known group comparisons and constructs for the patient group as a whole. Finally, the factor structure of the questionnaire was extracted by performing exploratory factor analysis. Results: All of the scales in the questionnaire showed good test-retest reliability (i.e. intraclass correlations between test and retest scores were > 0.7). All of the scales met the minimal criteria (0.7) for internal consistency and Cronbach's-alpha ranged 0.71-0.93. Furthermore, results from a discriminate validity evaluation showed that the questionnaire could be used to discriminate between subgroups of the patients. Finally, a principal component analysis of the disease-specific scales indicated that this part of the questionnaire could be summarized into an 11 factor structure that jointly accounted for 79.81% of the variance. Conclusion: The Iranian version of the KDQOL-SF questionnaire is both highly reliable and valid for use with Iranian patients on haemodialysis.