Purpose: To develop a Japanese version of the Expanded Prostate Cancer Index Composite (EPIC): originally designed to measure the Quality of Life of localized prostate cancer patients, after careful assessments of cross-cultural equivalence, face validity and practically.
Methods: We translated the original version that consisted of 50 items into a preliminary Japanese version. This multi-stage procedure included a forward-translation, back-translation and discussion with the original developer. Additionally, we tested the preliminary Japanese version on 11 localized prostate cancer patients and identified problems with its cross-cultural equivalence, practicality. Based on the findings of this pretest, we revised the Japanese version. Consensus by discussion among all researchers was obtained through out this process.
Results: The original developer reviewed the back-translation of the preliminary Japanese version: some wording was revised. In the pretest, the average age of patients was 68.8 years old. Four of the sexual subscale showed over 10 percent missing data. In five items, all patients chose identical answers. We conducted an in-depth qualitative investigation of these items. The average response time was 11.7 minutes. We revised the Japanese to reflect patients' opinions as much as possible. Items which were showed problems in terms of cross-cultural adaptation included questions measuring 'bother' and two items of the sexual subscale. The wordings of these items were revised so that Japanese patients could easier understand them. We ensured that the original developer's intentions remained the same. The original developed approved all revisions.
Conclusion: We translated and adapted the original EPIC to the Japanese culture. The Japanese version of EPIC was found to be functional in the pretest.