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Updated: May 16, 2026
05:21
Computerized Adaptive Testing System of Functional Assessment of Stroke
Published on: January 7, 2019
Testing for differential item functioning within the EQ-5D
David K Whynes1, Nikola Sprigg2, James Selby3
1School of Economics (DKW), University of Nottingham, Nottingham, UK
Summary
Differential item functioning (DIF) was assessed in the EQ-5D quality-of-life instrument. Regional differences significantly impacted EQ-5D scores, while proxy vs. patient reporting showed minimal impact.
Area of Science:
- Health Services Research
- Psychometrics
- Clinical Trials
Background:
- The EQ-5D is a widely used health-related quality-of-life instrument.
- Differential Item Functioning (DIF) can bias instrument scores when subgroups respond differently.
Purpose of the Study:
- To investigate DIF in the EQ-5D instrument within an acute stroke clinical trial.
- To examine DIF related to geographical region and patient-proxy reporting.
Main Methods:
- Analysis of 1462 patient records from a large clinical trial (ISRCTN 99414122).
- Mapping clinical outcome measures (modified Rankin Scale, Barthel Index, Zung Depression Scale) to EQ-5D index scores.
- Inclusion of dummy variables for proxy responses and treatment region (UK, Asia, rest of world).
Main Results:
- Proxies reported more health problems than patients for similar clinical states, but this did not significantly alter mean EQ-5D index scores.
- Significant divergence in reported problem severity distributions by geographical region, leading to different EQ-5D index scores.
- Mean EQ-5D index scores were significantly higher for UK responses compared to Asia and the rest of the world.
Conclusions:
- Geographical region is a significant factor contributing to DIF in the EQ-5D instrument.
- While proxy reporting showed some differences, it did not substantially impact overall EQ-5D index scores in this cohort.
- Findings highlight the need to consider regional variations when interpreting EQ-5D scores in international clinical research.
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