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Nonunique Solutions to the Likelihood Equation for the Three-Parameter Logistic Model

Published online by Cambridge University Press:  01 January 2025

Wendy M. Yen*
Affiliation:
CTB Macmillan/McGraw-Hill
George R. Burket
Affiliation:
CTB Macmillan/McGraw-Hill
Robert C. Sykes
Affiliation:
CTB Macmillan/McGraw-Hill
*
Requests for reprints should be sent to Wendy M. Yen, CTB Macmillan/McGraw-Hill, 2500 Garden Road, Monterey, CA 93940.

Abstract

Samejima identified the possibility of multiple solutions to the likelihood equation (multiple maxima in the likelihood function) for estimating an examinee's trait value for the three-parameter logistic model. In the practical applications that Lord studied, he found that multiple solutions did not occur when the number of items was ≥20. In the present paper, fourteen multiple-choice achievement tests with from 20 to 50 items were examined to see if it was possible for them to produce item response vectors with multiple maxima; such vectors were found for all the tests. Examination of response vectors for large groups of real examinees found that from 0 to 3.1% of them had response vectors with multiple maxima. The implications of these results for multiple-choice tests are discussed.

Type
Original Paper
Copyright
Copyright © 1991 The Psychometric Society

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