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DIFferential Testlet Functioning Definitions and Detection DIF SAT

Wainer, Howard; Sireci, Stephen G.; Thissen, David
Publication Year:
Report Number:
RR-91-21, PSRTR-91-09
ETS Research Report
Document Type:
Page Count:
Subject/Key Words:
Differential Item Functioning (DIF), SAT, Test Construction, Test Format, Testlets


It is sometimes sensible to think of the fundamental unit of test construction as being larger than an individual item. This unit, dubbed the testlet, must pass muster in the same way that items do. One criterion of a good item is the absence of DIF--the item must function in the same way in all important subpopulations of examinees. In this paper we define what we mean by testlet DIF and provide a statistical methodology to detect it. This methodology parallels the IRT-based likelihood ratio procedures explored previously by Thissen, Steinberg and Wainer (1988, in press). We illustrate this methodology with analyses of data from a testlet-based experimental version of the Scholastic Aptitude Test.

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