Session Information
Date: Wednesday, June 22, 2016
Session Title: Clinical Phenomenology and Rating Scales
Session Time: 12:00pm-1:30pm
Objective: Test if DIF due to gender or age is present in MDS-UPDRS items.
Background: Testing a rating scale for DIF is a core step in comprehensive validation methodology. DIF occurs for the MDS-UPDRS when the probability of item scores differs among people with similar levels of parkinsonism but belong to different groups on a secondary trait (gender or age). If DIF is present, interpretation of an item score needs to include consideration of the secondary trait as well as parkinsonism severity. There are 2 types of DIF: uniform (U-DIF), where the influence on item scores by the secondary trait is constant over all levels of parkinsonism; and non-uniform (NU-DIF), where the influence on item scores by the secondary trait varies across levels of parkinsonism.
Methods: Using the cross-sectional MDS-UPDRS translation database (N=5,476), we first confirmed unidimensionality of each MDS-UPDRS Part using CFA techniques. We then tested the impact of gender and age (28-51, 52-75, 76-97 yrs) on U-DIF and NU-DIF for each Part. We required that two independent methods, MIMIC and lordif, both identified item-specific DIF to qualify for consideration. Because very few of those patients studied had scores of 4, we collapsed scores of 3 and 4 into one category to allow the methods to converge mathematically. The DIF impact was determined by McFadden pseudo R2 cut-offs (large, moderate, negligible) and considered items pertinent if they exceeded the criteria beyond negligible R2 > 0.035.
Results: For most MDS-UPDRS items, there was no gender- or age-based NU-DIF or U-DIF. For gender, if DIF occurred, impact was always negligible. For age, no item met the criteria for pertinent impact of NU-DIF. Two items from Part 2 (Motor Experiences of Daily Living) showed U-DIF of moderate impact: 2.11 Getting out of bed (R2=0.060) and 2.12 Walking and balance (R2=0.053).
Conclusions: Gender has no pertinent DIF impact for the MDS-UPDRS, allowing the scale to be utilized as a core outcome measure across populations with varying gender distributions. For age, items 2.11 and 2.12 demonstrated pertinent U-DIF. As subject age increases, higher scores on these two activities occur at all levels of overall Part 2 severity. Interpretation of these items needs to include consideration of patient age as well as parkinsonism in evaluating MDS-UPDRS Motor Experiences of Daily Living (Part 2).
To cite this abstract in AMA style:
C.G. Goetz, L. Wang, G.T. Stebbins, B.C. Tilley, S. Luo. Gender and age-based differential item functioning (DIF) analysis of MDS-UPDRS [abstract]. Mov Disord. 2016; 31 (suppl 2). https://www.mdsabstracts.org/abstract/gender-and-age-based-differential-item-functioning-dif-analysis-of-mds-updrs/. Accessed December 9, 2024.« Back to 2016 International Congress
MDS Abstracts - https://www.mdsabstracts.org/abstract/gender-and-age-based-differential-item-functioning-dif-analysis-of-mds-updrs/