Differential item functioning in the Unified Dyskinesia Rating Scale (UDysRS).
OBJECTIVE: Test if differential item functioning due to gender, age, race/ethnicity, or education impacts Unified Dyskinesia Rating Scale scores. BACKGROUND: Testing rating scales for differential item functioning is a core validation step. If differential item functioning exists, interpretation of item scores must consider secondary influences on dyskinesia ratings. METHODS: Using Unified Dyskinesia Rating Scale translation databases (N = 3,132), we tested uniform and nonuniform differential item functioning. We required confirmation by two independent methods and considered differential item functioning pertinent if McFadden pseudo R2 magnitude statistics exceeded negligible ratings. RESULTS: No age, race/ethnicity, or education nonuniform differential item functioning was identified. Gender nonuniform differential item functioning occurred for 2 items, both with negligible magnitude. Gender, race, and education uniform differential item functioning was observed for multiple items, all with negligible magnitude. CONCLUSIONS: The Unified Dyskinesia Rating Scale items effectively capture dyskinesia severity without pertinent gender, age, race/ ethnicity, or education influence. © 2017 International Parkinson and Movement Disorder Society.
Luo, S; Liu, Y; Teresi, JA; Stebbins, GT; Goetz, CG
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