, Volume 67, Issue 1, pp 123–136 | Cite as

Equivalent linear logistic test models

  • Timo M. Bechger
  • Huub H. F. M. Verstralen
  • Norman D. Verhelst


This paper is about the Linear Logistic Test Model (LLTM). We demonstrate that there are infinitely many equivalent ways to specify a model. An implication is that there may well be many ways to change the specification of a given LLTM and achieve the same improvement in model fit. To illustrate this phenomenon, we analyze a real data set using a Lagrange multiplier test for the specification of the model. This Lagrange multiplier test is similar to the modification index used in structural equation modeling.

Key words

item response theory (IRT) linear logistic test model Lagrange multiplier test 


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Copyright information

© The Psychometric Society 2002

Authors and Affiliations

  • Timo M. Bechger
    • 1
  • Huub H. F. M. Verstralen
    • 1
  • Norman D. Verhelst
    • 1
  1. 1.Cito, National Institute for Educational MeasurementThe Netherlands

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