Negligible impact of differential item functioning between Black and White dialysis patients on the Kidney Disease Quality of Life 36-item short form survey (KDQOLTM-36)
Black dialysis patients report better health-related quality of life (HRQOL) than White patients, which may be explained if Black and White patients respond systematically differently to HRQOL survey items.
We examined differential item functioning (DIF) of the Kidney Disease Quality of Life 36-item (KDQOLTM-36) Burden of Kidney Disease, Symptoms and Problems with Kidney Disease, and Effects of Kidney Disease scales between Black (n = 18,404) and White (n = 21,439) dialysis patients. We fit multiple group confirmatory factor analysis models with increasing invariance: a Configural model (invariant factor structure), a Metric model (invariant factor loadings), and a Scalar model (invariant intercepts). Criteria for invariance included non-significant χ2 tests, > 0.002 difference in the models’ CFI, and > 0.015 difference in RMSEA and SRMR. Next, starting with a fully invariant model, we freed loadings and intercepts item-by-item to determine if DIF impacted estimated KDQOLTM-36 scale means.
ΔCFI was 0.006 between the metric and scalar models but was reduced to 0.001 when we freed intercepts for the burdens and symptoms and problems of kidney disease scales. In comparison to standardized means of 0 in the White group, those for the Black group on the Burdens, Symptoms and Problems, and Effects of Kidney Disease scales were 0.218, 0.061, and 0.161, respectively. When loadings and thresholds were released sequentially, differences in means between models ranged between 0.001 and 0.048.
Despite some DIF, impacts on KDQOLTM-36 responses appear to be minimal. We conclude that the KDQOLTM-36 is appropriate to make substantive comparisons of HRQOL between Black and White dialysis patients.
KeywordsHealth-related quality of life KDQOL-36 Measurement invariance Differential item functioning
Confirmatory factor analysis
Comparative fit index
Centers for Medicare and Medicaid Services
Differential item functioning
Dialysis outcomes and practice patterns study
End-stage renal disease
Health-related quality of life
Kidney Disease Component Summary
Kidney Disease Quality of Life 36-item survey
Mental Component Summary
Physical Component Summary
Root mean squared error of approximation
Standardized root mean square residual
Weighted least squares with mean and variance adjustment
We are grateful to Dori Schatell and Ryne Estabrook for their insightful suggestions on this manuscript. There was no direct financial support for the research reported in this manuscript.
This study was not funded.
Compliance with ethical standards
Conflict of interest
All authors declare no conflict of interest.
This article does not contain any studies with human subjects performed by any of the authors.
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