Abstract
Establishing measurement equivalence is important because inaccurate assessment may lead to incorrect estimates of effects in research, and to suboptimal decisions at the individual, clinical level. Examination of differential item functioning (DIF) is a method for studying measurement equivalence. An item (i.e., one question in a longer scale) exhibits DIF if the item response differs across groups (e.g., gender, race), controlling for an estimate of the construct being measured. A distinction between applications in health, as contrasted with other settings such as educational and aptitude testing, is that there are many health-related constructs and multiple measures of each, few of which have received much critical evaluation. Discussed in this article are several methods for detection of differential item functioning (DIF), including non-parametric and parametric methods such as logistic regression, and those based on item response theory. Basic definitions and criteria for DIF detection are provided, as are steps in performing the analyses. Recommendations are presented and future directions discussed.
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Acknowledgements
The authors thank Douglas Holmes for his review of several versions of this manuscript. The authors also thank Paul Crane and two anonymous reviewers and the editor for their helpful comments related to an earlier version of this manuscript. These analyses were conducted on behalf of the Statistical Coordinating Center to the Patient Reported Outcomes Information System (PROMIS) (AR052177). Funding for analyses was provided in part by the National Institute on Aging, Resource Center for Minority Aging Research at Columbia University (AG15294), and by the National Cancer Institute through the Veteran’s Administration Measurement Excellence and Training Resource Information Center (METRIC). An earlier version of this paper was presented at the National Institutes of Health Conference on Patient Reported Outcomes, Bethesda, June 2004.
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The opinions expressed in this article are those of the authors. No official endorsement by AHRQ or the Department of Health and Human Services is intended or should be inferred.
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Teresi, J.A., Fleishman, J.A. Differential item functioning and health assessment. Qual Life Res 16 (Suppl 1), 33–42 (2007). https://doi.org/10.1007/s11136-007-9184-6
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DOI: https://doi.org/10.1007/s11136-007-9184-6