[The interoperability of IIEF-5 with EPIC-26 : Sexual function after radical prostatectomy]

In the past, the IIEF‑5 (International Index of Erectile Function 5 ) was predominantly used to measure erectile function in prostate cancer patients. Following international developments, the domain "sexuality" of the EPIC-26 (Expanded Prostate Cancer Index Composite 26) is increasingly used in Germany.

The aim of this work is to create a practicable comparison of the domain "sexuality" of the EPIC-26 with the IIEF‑5 for treatment in Germany. This is particularly necessary for the evaluation of historical patient collectives.

For the evaluation, 2123 patients with prostate cancer confirmed by biopsy from 2014-2017 who completed both the IIEF‑5 and the EPIC-26 were considered. Linear regression analyses are calculated to convert IIEF‑5 sum scores to EPIC-26 sexuality domain scores.

The correlation between IIEF‑5 and the EPIC-26 domain score "sexuality" was 0.74, suggesting a high degree of content convergence between the constructs measured. While the standard error of the predicted values is relatively small, the prediction intervals are very wide. For example, for the critical IIEF‑5 value of 22, the predicted value is 78.88 with a 95% prediction interval of 55.09 to 102.66.

IIEF‑5 and the Sexuality scale of the EPIC-26 measure a similar construct. The analysis shows that conversion of individual values is associated with great uncertainty. However, at the group level, the observed EPIC-26 "sexuality" score could be predicted quite accurately. This opens up the possibility of comparing the erectile function of cohorts of patients/test persons, even if this was collected with different measuring instruments.