The Clinically Important Difference on the Unified Parkinson's Disease Rating Scale

Abstract

A clinically important difference (CID) is the amount of change on a measure that patients can recognize and value.¹ Growing interest in CIDs stems from a greater emphasis on evidence-based and patient-centered medicine.² Large randomized clinical trials frequently show significant differences on outcome measures that are so small that clinicians are unsure how to apply them to clinical decision making.³ The Movement Disorder Society Task Force on Rating Scales for Parkinson's Disease highlighted the importance of identifying thresholds on the Unified Parkinson's Disease Rating Scale (UPDRS) that represent clinically relevant differences.^4,5 The US Food and Drug Administration also described the need to define minimally important differences on patient-reported outcome measures used to support the labeling claims of medical products.⁶