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Increasing Item Complexity: A Possible Cause of Scale Shrinkage for Unidimensional Item Response Theory

Published online by Cambridge University Press:  01 January 2025

Wendy M. Yen
Wendy M. Yen*
Affiliation:
CTB/McGraw-Hill
*
Requests for reprints should be sent to Wendy M. Yen, CTB/McGraw-HilI, 2500 Garden Road, Monterey, CA 93940.
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Abstract

When the three-parameter logistic model is applied to tests covering a broad range of difficulty, there frequently is an increase in mean item discrimination and a decrease in variance of item difficulties and traits as the tests become more difficult. To examine the hypothesis that this unexpected scale shrinkage effect occurs because the items increase in complexity as they increase in difficulty, an approximate relationship is derived between the unidimensional model used in data analysis and a multidimensional model hypothesized to be generating the item responses. Scale shrinkage is successfully predicted for several sets of simulated data.

Keywords

item response theorymultidimensional modelsscaling
Type
Original Paper
Information
Psychometrika , Volume 50 , Issue 4 , December 1985 , pp. 399 - 410
Copyright
Copyright © 1985 The Psychometric Society

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Footnotes

The author is grateful to Robert Mislevy for kindly providing a copy of his computer program, RESOLVE.

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