Elsevier

Urology

Volume 54, Issue 2, August 1999, Pages 346-351
Urology

Adult Urology
Diagnostic evaluation of the erectile function domain of the international index of erectile function

https://doi.org/10.1016/S0090-4295(99)00099-0Get rights and content

Abstract

Objectives. To evaluate the erectile function (EF) domain of the International Index of Erectile Function (IIEF) as a diagnostic tool to discriminate between men with and without erectile dysfunction (ED) and to develop a clinically meaningful gradient of severity for ED.

Methods. One thousand one hundred fifty-one men (1035 with and 116 without ED) who reported attempting sexual activity were evaluated using data from four clinical trials of sildenafil citrate (Viagra) and two control samples. The statistical program Classification and Regression Trees was used to determine optimal cutoff scores on the EF domain (range 6 to 30) to distinguish between men with and without ED and to determine levels of ED severity on the EF domain using the IIEF item on sexual intercourse satisfaction.

Results. For a 0.5 prevalence rate of ED, the optimal cutoff score was 25, with men scoring less than or equal to 25 classified as having ED and those scoring above 25 as not having ED (sensitivity 0.97, specificity 0.88). Sensitivity analyses revealed a robust statistical solution that was well supported with different assumed prevalence rates and several cross-validations. The severity of ED was classified into five categories: no ED (EF score 26 to 30), mild (EF score 22 to 25), mild to moderate (EF score 17 to 21), moderate (EF score 11 to 16), and severe (EF score 6 to 10). Substantial agreement was shown between these predicted and “true” classes (weighted kappa 0.80).

Conclusions. The EF domain possesses favorable statistical properties as a diagnostic tool, not only in distinguishing between men with and without ED, but also in classifying levels of ED severity. Clinical validation with self-rated assessments of ED severity is warranted.

Section snippets

EF domain

The six items on the EF domain include detailed questions concerning erection frequency, erection firmness, penetration ability, maintenance frequency, maintenance ability, and erection confidence.1 All analyses were restricted to baseline (pretreatment) data. The enrolled samples in the analyses were composed of men who reported having had sexual activity at least once during the 4 weeks before their baseline responses to the questions. Each item was therefore based on a 5-point Likert scale.

Single cutoff scores

Table II shows the results for the different assumed prevalence rates of ED for the sample data. The optimal cutoff was 22 for prevalence rates of ED from 0.20 to 0.30, 25 for prevalence rates from 0.35 to 0.60, and 26 for a prevalence rate of 0.65. Diagnostic values for the optimal cutoff scores gave relatively high discrimination and, although the kappa values were lower for the lowest three prevalence rates, were generally similar across prevalence rates. All cross-validation results (not

Comment

The CART algorithm, which we applied to establish optimal cutoff scores, has been extensively applied to a wide range of clinical decision aids in published reports.9, 10 A cutoff score does not need to be optimal, however, to have adequate diagnostic characteristics; several cutoffs may be appropriate.8, 9, 10

We used only the EF domain of the IIEF to diagnose the presence and severity of ED. In general, favorable results were obtained that were easily interpreted. When the risk factors in

Conclusions

These data support the validity of the EF domain of the IIEF as a diagnostic tool in clinical settings for grading degrees of severity of ED and for distinguishing between men with and without the disorder. The IIEF is currently widely used in clinical trials of ED; the proposed classification would potentially enhance its use in both research and clinical settings. The proposed classification system, however, should not be viewed as a perfect diagnostic discriminator. The classifications are

Acknowledgements

To Drs. Murray C. Maytom, Frances Quirk, and Pierre A. Wicker, all from Pfizer Inc., for their helpful input.

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