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A Study of the Temporal Stability of IRT Item Parameter Estimates IRT SAT

Cook, Linda L.; Eignor, Daniel R.; Petersen, Nancy S.
Publication Year:
Report Number:
ETS Research Report
Document Type:
Page Count:
Subject/Key Words:
Achievement Tests, Equated Scores, Item Response Theory (IRT), Mathematical Models, Scholastic Aptitude Test (SAT)


This research report focuses on the stability of item response theory (IRT) item parameter estimates when the items are calibrated on two different samples of examinees who have responded to the items at two different points in time, i.e., the temporal stability of the parameter estimates. Parameter estimates obtained from SAT-verbal and SAT-mathematical were more likely to exhibit stability over time than those obtained for achievement tests of Biology or American History and Social Studies. Lack of stability of item parameter estimates appeared to be more closely related to differences in ability among calibration samples than to the lapse of time between administrations of the test, which, in the study, ranged from 14 to 52 months. It should be noted, however, that for the particular tests studied, ability differences in calibration samples appeared to be unrelated to time differences between administrations. This may not be typical of other testing situations, where ability differences in the calibration samples can be directly related to length of time between test administrations. This could be brought about, for example, by changes in curricular emphasis. (86pp.)

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