Exploring the Content Validity of the Unified Wilson Disease Rating Scale: Insights from Qualitative Research

Introduction: Wilson disease (WD) is a rare metabolic disorder of impaired copper transport manifesting in hepatic, neurological, and psychiatric symptoms. To evaluate the clinical symptoms of WD in clinical trials, a group of clinicians created the Unified Wilson Disease Rating Scale (UWDRS). Content validity of this scale has not been established. The aim of this study was to evaluate the content validity of the UWDRS Part II from the patient perspective.

Methods: This study utilized multiple qualitative research methods including concept elicitation interviews, concept/instrument mapping, and cognitive debriefing interviews.

Results: Concept elicitation interviews with a sample of patients with WD and one or more neurological signs/symptoms identified several signs, symptoms, and impacts related to neurological dysfunction, strengthening our understanding of the importance of the neurological aspects of the WD patient experience. Mapping neurological concepts to Part II and III items of the UWDRS showed complete coverage of all salient neurological concepts and near complete coverage of all neurological concepts reported by patients in concept elicitation interviews. Item debriefing of Part II of the UWDRS revealed that patients generally found the items clear and personally relevant to their experience with WD.

Conclusion: Overall, the findings from this study provide evidence for the content validity of the UWDRS Part II and supportive evidence for the content validity of Part III. The UWDRS should be used in conjunction with additional clinical outcomes assessments, specifically those evaluating the hepatic and psychiatric signs/symptoms of WD, to provide a comprehensive evaluation of the WD patient experience.