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The Effect of the Probability of Correct Response on the Variability of Measures of Differential Item Functioning DIF

Zwick, Rebecca J.
Publication Year:
Report Number:
RR-94-44, PSRTR-94-04
ETS Research Report
Document Type:
Page Count:
Subject/Key Words:
Adaptive Testing, Differential Item Functioning (DIF), Item Analysis, Item Response Theory, Mantel-Haenszel Technique, Rasch Model


The Mantel-Haenszel (MH; 1959) approach of Holland and Thayer (1988) is a well-established method for assessing differential item functioning (DIF). The formula for the variance of the MH DIF statistic is based on work by Phillips and Holland (1987) and Robins, Breslow, and Greenland (1986). Recent simulation studies showed that the MH variances tended to be larger when items were administered to "examinees" who were randomly selected from a population than when items were administered adaptively. An analytic perspective shed some light on this puzzling result. Although the general form of the MH variance is complex and does not provide an intuitive understanding of the phenomenon, application of certain Rasch model assumptions yields a simple expression that appears to explain the difference in variances for adaptive versus nonadaptive administration. (18pp.)

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