Modified Likelihood-Based Item Fit Statistics for the Generalized Graded Unfolding Model  

Oleh:

Roberts, James S.

Jenis: Article from Journal - ilmiah internasional
Dalam koleksi: Applied Psychological Measurement vol. 32 no. 5 (Jul. 2008), page 407-423.
Topik: generalized graded unfolding model; GGUM; item fit; item response theory
Fulltext: 407.pdf (190.51KB)

Isi artikel

Orlando and Thissen (2000) developed an item fit statistic for binary item response theory (IRT) models known as S -X2. This article generalizes their statistic to polytomous unfolding models. Four alternative formulations of S -X2 are developed for the generalized graded unfolding model (GGUM). The GGUMis a unidimensional IRT model for unfolding polytomous responses. It yields single-peaked, nonmonotonic item characteristic curves that predict a higher item score to the extent that an individual is located close to an itemon the underlying latent continuum.A simulation was performed to examine the characteristics of these new item fit indices under the GGUM, as well as a traditional likelihood ratio w2 test (G2). All variants of S -X2 exhibited reasonable Type I error rates, but that forG2 was more erratic. The new indices exhibited variable power to detect misfit. Two new itemfit tests are recommended for use based on simulation results.

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