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A Note on the Reliability Coefficients for Item Response Model-Based Ability Estimates

Published online by Cambridge University Press:  01 January 2025

Seonghoon Kim*
Affiliation:
Keimyung University
*
Requests for reprints should be sent to Seonghoon Kim, Department of Education, Keimyung University, 1095 Dalgubeoldaero, Dalseo-Gu, Daegu 704-701, South Korea. E-mail: seonghoonkim@empal.com; seonghoonkim@kmu.ac.kr

Abstract

Assuming item parameters on a test are known constants, the reliability coefficient for item response theory (IRT) ability estimates is defined for a population of examinees in two different ways: as (a) the product-moment correlation between ability estimates on two parallel forms of a test and (b) the squared correlation between the true abilities and estimates. Due to the bias of IRT ability estimates, the parallel-forms reliability coefficient is not generally equal to the squared-correlation reliability coefficient. It is shown algebraically that the parallel-forms reliability coefficient is expected to be greater than the squared-correlation reliability coefficient, but the difference would be negligible in a practical sense.

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Type
Article
Copyright
Copyright © 2011 The Psychometric Society

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