Cultural adaptation and validation of the Chinese version of the expanded prostate cancer index composite

Aim: The expanded prostate cancer index composite (EPIC) is a widely adopted instrument for the quality of life of patients with prostate cancer. We aimed to create a Chinese version of EPIC to further research in the Chinese-speaking population. Methods: A prototype was created by forward-backward translations and revisions. During cultural adaptation, 15 participants were interviewed after they had completed the prototype. A few issues highlighted included confusion related to the question format, subject non-familiarity with the Chinese term for "hot flashes," and the use of the Chinese term for "breast" as a strictly female body part. A pilot version was created based on the cultural adaptation findings. Validation of the pilot version was performed by having 50 participants complete the Chinese EPIC and EORTC QLQ-c30 twice within a 4-week period. Test-retest reliability (Pearson's correlations and difference distribution) and internal consistency (Cronbach's alpha) were measured using SAS version 9.4. Results: Test-retest reliability values for the urinary, bowel, sexual and hormone domains were 0.71, 0.51, 0.51 and 0.66, respectively; subscale test-retest reliability ranged between 0.29 and 0.82. Internal consistency for domains was good with Cronbach's alpha ranging from 0.76 to 0.78 for the initial test and 0.67 to 0.85 for the retest. The performance of this version of EPIC was comparable to the validated EORTCQLQ-C30. Conclusion: The EPIC questionnaire was successfully translated into Chinese and was culturally adapted. The resultant Chinese version has high reliability and validity and will be an important tool for research on quality of life in the Chinese population.