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Model-Based Versus Empirical Equating of Test Forms

Defense Manpower Data Center, mary.quenette{at}osd.pentagon.mil

W. Alan Nicewander

Pacific Metrics, Inc.

Gary L. Thomasson

Defense Manpower Data Center

Model-based equating was compared to empirical equating of an Armed Services Vocational Aptitude Battery (ASVAB) test form. The model-based equating was done using item pretest data to derive item response theory (IRT) item parameter estimates for those items that were retained in the final version of the test. The analysis of an ASVAB test form indicated that the model-based equatings were nearly as accurate as the preliminary empirical equating, using the final empirical equating as a standard against which to judge the equatings. The fact that the model-based equatings so closely forecast the final ones suggests some indirect support for the assumptions commonly made in IRT analyses—that IRT models reasonably approximate human behavior when confronted by multiple-choice test items and a normal distribution for the latent trait being measured.

Key Words: item response theory • three-parameter logistic model • latent trait • unidimensionality • equipercentile equating • conversion tables • model fit

Applied Psychological Measurement, Vol. 30, No. 3, 167-182 (2006)
DOI: 10.1177/0146621605278816


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