Missingness in the expanded prostate cancer index short form (EPIC-26) - prevalence, patterns, and explanatory factors.

Questions 13.b. and 13.a. might be considered female-specific symptoms, thus difficult to comprehend unless patients had already experienced side effects from androgen deprivation therapy. Questions 10. and 8.b. might be difficult to answer if the patient has been sexually inactive. To improve the measure's validity, the questionnaire's hormonal section requires additional explanation that the inquired symptoms are common treatment side effects of anti-androgen therapy; questions 8-10 require a not-applicable category for sexually inactive patients.