An approach to cultural adaptation and validation: the Intermittent Claudication Questionnaire.

The objective of this study was to perform a cultural adaptation and define the validity of the Turkish version of the Intermittent Claudication Questionnaire (ICQ) in order to provide a practical instrument for the evaluation of the impact of intermittent claudication (IC) on patients' quality of life and response to therapy. A standard 'forward-backward' translation method was used to translate the questionnaire into Turkish. Reliability was assessed by internal consistency of the questionnaire reporting Cronbach's alpha coefficient, test-retest reliability that was assessed with the intraclass correlation between instrument scores over time and with the Spearman-Brown coefficient as a variant of split-half reliability. Validity was examined by correlation of the ICQ with the scores of the SF-36 and its eight domains. Eighty-four patients (mean age, 60.7 +/- 7.3 years; male, 57%) were given the ICQ and a final completion rate of 98.8% (83 patients) was reached. The mean total ICQ score was 39.1 +/- 21.8 (SD) (0-100) for the first application of the questionnaire. Thirty patients out of the eligible 83 completed the questionnaire at two time points with a 1-day interval. For the retest, the total ICQ score was 40.6 +/- 26.1 (4.7-97.2). The total SF-36 score of all the study patients was 33.8 +/- 20.7 (3.0-81.0). Cronbach's alpha was 0.95; the Spearman-Brown coefficient was 0.92; and the intraclass correlation coefficient for the two measurements was 0.91. For the total score and for the scores of domains except the emotional role domain, the correlations were high and all the correlations were statistically significant. In conclusion, the Turkish version of the ICQ, which is a disease-specific, self-administered, and practical instrument, is reliable and valid. We recommend its use to assess the effect of IC on the quality of life of patients in clinical trials and in daily clinical practice.