John D Peipert1,2,3, Peter Bentler4, Kristi Klicko5, Ron D Hays6. 1. Department of Medical Social Sciences, Feinberg School of Medicine, Northwestern University, 625 N. Michigan Ave., Suite 2700, Chicago, IL, 60611, USA. john.peipert@northwestern.edu. 2. Division of Nephrology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, USA. john.peipert@northwestern.edu. 3. Terasaki Research Institute, University of California, Los Angeles, Los Angeles, CA, USA. john.peipert@northwestern.edu. 4. Departments of Psychology and Statistics, University of California, Los Angeles, Los Angeles, CA, USA. 5. Medical Education Institute, Inc., Madison, WI, USA. 6. Division of General Internal Medicine and Health Services Research, University of California, Los Angeles, Los Angeles, CA, USA.
Abstract
PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.
PURPOSE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.
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