Psychometric performance of the incontinence quality-of-life questionnaire among patients with overactive bladder and urinary incontinence

Abstract

Background: The Incontinence Quality-of-Life Instrument (I-QOL) is a condition-specific questionnaire that assesses the health-related QOL impact of urinary incontinence, but it has not been validated in patients with overactive bladder (OAB) who have been inadequately managed by anticholinergic therapy.

Objective: This study assessed the reliability and validity of the I-QOL among patients with OAB with urinary incontinence.

Methods: I-QOL scores were analyzed from a Phase II study that compared the efficacy and tolerability of onabotulinumtoxinA and placebo. Conceptual framework was confirmed via confirmatory factor analysis. Reliability was assessed using Cronbach's alpha and intraclass correlation coefficients (ICCs). Validity was tested by comparing I-QOL scores to tertiles of urinary symptom severity. Effect size statistics estimated the ability of the I-QOL to detect change. Responder analysis with cumulative distribution function was plotted to show differentiation between treatment groups with respect to I-QOL scores.

Results: Comparative fit indices ranged from 0.87 to 0.99 on the confirmatory factor analysis. I-QOL scores showed high internal consistency (0.86 ≤ Cronbach's α ≤ 0.93), good test-retest reliability (0.68 ≤ ICC ≤ 0.84), and good differentiation between tertiles of increasing urinary symptom severity (all, P ≤ 0.002). Significant differences in I-QOL change scores were noted between responders and nonresponders across all responder definitions (all, P < 0.001) and corresponded with large effect sizes among responders to treatment (1.34 ≤ effect size ≤ 2.82).

Conclusion: This study demonstrated that OAB with urinary incontinence affects health-related QOL and that the I-QOL reliably and validly measures these impacts.