Responsiveness and minimum important differences for the erection quality scale
We evaluated the responsiveness and treatment sensitivity of the Erection Quality Scale, and provided further psychometric validation of this scale.
Materials and Methods
An 8-week, placebo controlled, randomized clinical trial investigating the efficacy and safety of vardenafil in patients with erectile dysfunction was performed. The Erection Quality Scale, together with a number of other patient and partner questionnaires, was administered at a screening visit, at baseline, and weeks 4 and 8 of treatment. Erection Quality Scale responsiveness was investigated by evaluating treatment induced changes and modeling using ANCOVA. Internal consistency, convergent and discriminant validity, and minimum important difference of the Erection Quality Scale were also assessed.
Efficacy evaluations demonstrated that the Erection Quality Scale was sufficiently responsive to differentiate the treatment benefits of vardenafil compared with placebo. Internal consistency for the Erection Quality Scale total score was similar across visits, with values high enough to suggest reliability of items included in the scale. Discriminant validity of the Erection Quality Scale total score was demonstrated, with a high correlation with the erectile function domain of the International Index of Erectile Function (0.88, p <0.0001) and negligible correlations with clinical measures assumed to be unrelated to erection quality. All Erection Quality Scale total score comparisons substantially exceeded the 5-point minimum important difference estimate.
The Erection Quality Scale was responsive and internally consistent, and demonstrated convergent and discriminant validity. Furthermore, this instrument provided a unique contribution to the measurement of erection quality compared to the International Index of Erectile Function. This study provides strong evidence supporting the use of the Erection Quality Scale in clinical trials.