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Exploring Alternative Test Form Linking Designs With Modified Equating Sample Size and Anchor Test Length IRT

Wang, Lin; Qian, Jiahe; Lee, Yi-Hsuan
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ETS Research Report
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Subject/Key Words:
Anchor Test Length, Equating Sample Size, Equating to a Calibrated Item Pool Design, Complete Grouped Jackknifing, Item Response Theory (IRT)


The purpose of this study was to evaluate the combined effects of reduced equating sample size and shortened anchor test length on item response theory (IRT)-based linking and equating results. Data from two independent operational forms of a large-scale testing program were used to establish the baseline results for evaluating the results from two alternative designs. Under the two alternative designs, two simulated conditions were created from the original data. Under one condition, we reduced the equating sample size (from about 2,000 to about 1,000) per anchor item and shortened the anchor test length (by half) per equating sample. Under the other condition, we reduced the sample size (from about 2,000 to about 1,000) per anchor item only. A complete grouped jackknife replication method was used to estimate the standard errors of the linking and equating procedures from 100 jackknife replicate samples; the complete procedures included IRT calibrations, item parameter scaling, and IRT true score equating. The findings from a comparison of the results from the two simulated conditions and the baseline results showed that neither alternative design had any practical impact on the linking and equating results for either test form.

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