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Specifying the Characteristics of Linking Items Used for Item Response Theory Item Calibration IRT

Wingersky, Marilyn S.; Cook, Linda L.; Eignor, Daniel R.
Publication Year:
Report Number:
ETS Research Report
Document Type:
Page Count:
Subject/Key Words:
Equated Scores, Item Analysis, Item Response Theory (IRT), LOGIST


The purpose of this study was to investigate the effects on IRT true-score equating results of the characteristics of the linking items that are used to place parameter estimates for items contained in two test editions on the same scale prior to equating. The study was carried out using the three-parameter logistic item response theory model and Monte Carlo procedures. So that the simulated data reflected actual test data, the true item parameters were taken from the estimated parameters obtained from LOGIST calibrations of item responses obtained from selected administrations of the verbal sections of the College Board Scholastic Aptitude Test (SAT-V). The results of the study indicate that, 1) for data such as those simulated for this study, improved equating results are obtained if longer linking tests are used with a uniform distribution of examinee ability; 2) it maybe more important to evaluate the relative efficiency of the linking items, with respect to the total test, than it is to evaluate the size of the standard errors of estimation of the linking item parameter estimates; and 3) equating results, particularly those obtained using a characteristic curve transformation design, are affected by the presence of linking items that function differently for the two groups used to provide data for the equating and calibration, particularly for shorter linking tests. It appears that the quality of an equating depends to some extent on prior screening of linking tests and removal of items that function differently for the two groups. (106pp.)

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