The International Index of Erectile Function-6 as a tool for detecting subclinical erectile dysfunction: insights from latent variable modeling and item response theory

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BACKGROUND: In the diagnosis of erectile dysfunction (ED), the 5 + 1 erectile function domain of the International Index of Erectile Function (IIEF-6) is the reference screening tool, but its conventional sum-score scoring may mask subtle functional impairments in high-functioning men because of ceiling effects. AIM: To operationalize the detection of subclinical erectile dysfunction (SED) using latent variable modeling applied to the IIEF-6 and to validate SED as a distinct phenotype independent of ejaculatory and psychological confounders. METHODS: This cross-sectional analysis used the well-established database of the SEXCOVID study, including 1114 sexually active Italian men aged 18-65 years. Erectile function was assessed with the IIEF-6. Ordinal Structural Equation Modeling and Item Response Theory were applied to generate latent erectile function scores, which were linearly calibrated to standard clinical cutoffs. Anxiety, depressive symptoms, and premature ejaculation (PE) were assessed using validated questionnaires. OUTCOMES: Primary outcomes were score distribution properties, diagnostic reclassification rates, item discrimination parameters, and associations with psychological and ejaculatory measures. RESULTS: Raw IIEF-6 scores showed pronounced ceiling effects, whereas latent modeling restored variance and approximate normality. Latent scoring increased correlations between erectile function and anxiety and depression by 20.1% and 27.9%, respectively. Overall, 17.7% of subjects were diagnostically reclassified. Notably, 144 men (12.9%) classified as "No ED" by sum scores were reclassified as "Mild ED," defining the SED phenotype. High-discrimination items related to erection firmness and maintenance primarily drove reclassification. SED subjects did not differ from healthy controls in PE risk but showed mildly higher anxiety and depression levels. CLINICAL IMPLICATIONS: Latent scoring of the IIEF-6 identifies clinically relevant erectile instability that is not captured by conventional sum scores, enabling earlier preventive assessment. STRENGTHS AND LIMITATIONS: Strengths include advanced psychometric modeling and a large community sample; limitations include the cross-sectional design and self-reported measures. CONCLUSION: Latent variable modeling enhances the diagnostic sensitivity of the IIEF-6 and provides empirical support for SED as a distinct, measurable clinical entity.

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