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Impact of scaling methods on ability estimates.

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Zhu R, Lipner RS. — American Board of Internal Medicine

Presented: American Educational Research Association Meeting, May 2010

Abstract: To ensure the comparability of examinees’ ability scores across multiple forms of the test, a critical step is to place item parameters from different calibrations on a common scale. Concurrent calibration and linear transformation are the two scaling methods commonly used. In concurrent calibration, items administered to different groups of examinees are calibrated simultaneously and a common metric is produced automatically. A linear transformation requires separate calibrations and then uses the parameters of the linking items to determine the transformation function. The purpose of this study was to evaluate the effects of the two scale methods on the precision of ability estimates. Preliminary results showed that the two scaling methods were comparable, while concurrent calibration yielded slightly lower error.

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