To assess whether the translated Korean version of the International Index of Erectile Function (IIEF-5) developed by Rosen et al. (RIIEF-5) may be adapted for a Korean population to have cross-cultural equivalency to the original version.

A total of 151 patients with erectile dysfunction (ED) and 156 controls were prospectively studied. All the patients and controls had had sexual activity or attempted sexual intercourse within the 4-week period before completing the questionnaire. The Classification and Regression Trees program was used to select an optimal set of five items from the IIEF-15 (KIIEF-5) to discriminate between men with and without ED. Then, the optimal cutoff score for the diagnosis of ED was determined using the receiver operating characteristic curve. The optimal cutoff score, sensitivity, and specificity were also calculated using the RIIEF-5.

The KIIEF-5 consisted, in order of importance, of items 15, 5, 13, 4, and 2 from the IIEF-15. Item 7 in the original RIIEF-5 was replaced with item 13 in the new KIIEF-5. The optimal cutoff score proved to be 21, with a corresponding sensitivity and specificity of 0.97 and 0.91, respectively. For the original RIIEF-5, the optimal cutoff score was 21 and the corresponding sensitivity and specificity was 0.94 and 0.90, respectively.

Although the RIIEF-5 may be adapted for a Korean population, the KIIEF-5 can aid in decreasing the incidence of an incorrect diagnosis of ED and decreasing the number of undiagnosed cases of ED in this population. In addition, our findings suggest that the equivalence of psychometric properties does not imply cross-cultural equivalence.