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An Extension of the Partial Credit Model with an Application to the Measurement of Change

Published online by Cambridge University Press:  01 January 2025

Gerhard H. Fischer*
Affiliation:
University of Vienna
Ivo Ponocny
Affiliation:
University of Vienna
*
Requests for reprints or for the LPCM software (please send a formatted 3 1/2 inch diskette) should be directed to Gerhard H. Fischer, Institut für Psychologic, Liebiggasse 5, A-1010 Wien (Vienna), Austria, e-mail [email protected].

Abstract

The partial credit model is considered under the assumption of a certain linear decomposition of the item × category parameters δih into “basic parameters” αj. This model is referred to as the “linear partial credit model”. A conditional maximum likelihood algorithm for estimation of the αj is presented, based on (a) recurrences for the combinatorial functions involved, and (b) using a “quasi-Newton” approach, the so-called Broyden-Fletcher-Goldfarb-Shanno (BFGS) method; (a) guarantees numerically stable results, (b) avoids the direct computation of the Hesse matrix, yet produces a sequence of certain positive definite matrices Bk, k = 1, 2, ..., converging to the asymptotic variance-covariance matrix of the \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\hat \alpha _j $$\end{document}. The practicality of these numerical methods is demonstrated both by means of simulations and of an empirical application to the measurement of treatment effects in patients with psychosomatic disorders.

Type
Original Paper
Copyright
Copyright © 1994 The Psychometric Society

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Footnotes

The authors thank one anonymous reviewer for his constructive comments. Moreover, they thankfully acknowledge financial support by the Österreichische Nationalbank (Austrian National Bank) under Grant No. 3720.

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