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Effect of Group Heterogeneity on Item Parameters

Published online by Cambridge University Press:  01 January 2025

Harold Gulliksen
Harold Gulliksen*
Affiliation:
Educational Testing Service
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Abstract

Most indexes of item validity and difficulty vary systematically with changes in the mean and variance of the group. Formulas are presented showing how certain item parameters will vary with these alterations in group mean and variance. Item parameters are also suggested which should remain invariant under such changes. These parameters are developed under two different assumptions: first, the assumption that the total distribution of the item ability variable is normal, and, second, that the distribution of the item ability variable for each array of the explicit selection variable is normal.

Type
Original Paper
Information
Psychometrika , Volume 16 , Issue 3 , September 1951 , pp. 285 - 296
Copyright
Copyright © 1951 The Psychometric Society

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Footnotes

*

The writer wishes to acknowledge helpful discussions of this paper with Paul Horst and Herbert S. Sichel who have worked on various aspects of the problem of invariant item parameters.

References

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