Establishing the Minimal Clinically Important Difference for the Wisconsin Stone Quality of Life Questionnaire Using Distribution- and Anchor-Based Methods

<b><i>Purpose:</i></b> The Wisconsin Stone Quality of Life (WISQOL) questionnaire is a survey-based tool that has been used to show worse health-related quality of life due to stone disease. The minimum clinically important difference threshold for determining whether changes in the WISQOL tool are meaningfully significant has not previously been estimated. Our study aimed to determine this threshold using distribution- and anchor-based methods. <b><i>Materials and Methods:</i></b> A retrospective single-center cohort of patients at a kidney stone clinic was administered the WISQOL questionnaire at initial and follow-up visits from January 2018 to November 2023. Baseline characteristics and WISQOL standardized scores and subdomain scores were recorded. Distribution-based estimates were calculated at the initial visit and at follow-up. Three anchor questions were used to create a global transition question scale. Cross-sectional, longitudinal within-group, and longitudinal between-group anchor-based estimates were calculated. <b><i>Results:</i></b> The cohort included 1197 individuals with both an initial clinic visit and a follow-up visit. The distribution-based minimum clinically important difference estimates ranged from 3.5 to 10.8. Cross-sectional anchor-based estimates ranged from 3.1 to 13.6. Within-group anchor-based estimates for improvement ranged from 8.5 to 10.3 and for deterioration ranged from 3.1 to 6.3. Between-group anchor-based estimates for improvement were 9.1 (adjusted confidence interval [CI]: 7.5-10.8) and for deterioration were 4.2 (adjusted CI: 2.3-6.1). <b><i>Conclusions:</i></b> A conservative threshold for clinical significance in total WISQOL score (standardized to scale of 0-100) is a difference of 9 for both improvement and deterioration. These findings can be used to further implement WISQOL in guiding clinical decision-making.