Qualiveen, a urinary-disorder specific instrument: 0.5 corresponds to the minimal important difference
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OBJECTIVE: This study assessed the interpretability of changes in Qualiveen, a specific health-related quality-of-life (HRQOL) questionnaire for urinary disorders (UD) in multiple sclerosis (MS) patients. Qualiveen has 30 items focusing on four aspects of patients' lives related to their urinary problems: bother with limitations (nine items), frequency of limitations (eight items), fears (eight items), and feelings (five items). Response options are framed as 5-point Likert-type scales, and scores on each domain range from 0 to 4. STUDY DESIGN AND SETTING: One hundred twenty-one MS patients with UD completed Qualiveen at baseline and 2-10 weeks later. At the second visit, patients also made global ratings of change in urinary HRQOL (GRC) with a 15-point scale from -7 to +7. We addressed the validity of GRC by examining its relationships with pre- and post-Qualiveen scores and determined the mean change in score on each Qualiveen domain associated with small, moderate, and large changes in the corresponding GRC. RESULTS: The correlation of the change score with the corresponding GRC was substantially stronger than the correlation with either pre- or post-Qualiveen score, establishing the validity of the GRC. In all domains, a within-patient change in Qualiveen score of approximately 0.5 (range: 0.36-0.72) represents the minimal important difference. A change in score of approximately 0.7 corresponds to a moderate change in quality of life (range: 0.55-0.86). CONCLUSIONS: These estimates will help in interpreting the results of subsequent studies that use Qualiveen to examine the impact of interventions designed to improve urinary-specific HRQOL.