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ERIC Number: ED510479
Record Type: Non-Journal
Publication Date: 2007-Jun
Pages: 30
Abstractor: As Provided
Reference Count: 36
An Investigation of the Performance of the Generalized S-X[superscript 2] Item-Fit Index for Polytomous IRT Models. ACT Research Report Series, 2007-1
Kang, Taehoon; Chen, Troy T.
ACT, Inc.
Orlando and Thissen (2000, 2003) proposed an item-fit index, S-X[superscript 2], for dichotomous item response theory (IRT) models, which has performed better than traditional item-fit statistics such as Yen's (1981) Q[subscript 1] and McKinley and Mill's (1985) G[superscript 2]. This study extends the utility of S-X[superscript 2] to polytomous IRT models, including the generalized partial credit model (GPCM: Muraki, 1992), partial credit model (PCM: Masters, 1982), and rating scale model (RSM: Andrich, 1978). The performance of the generalized S-X[superscript 2] in assessing item-model fit was studied in terms of empirical Type I error rates and power as compared to results obtained for G[superscript 2] provided by the computer program PARSCALE (Muraki & Bock, 1997). The results show that the generalized S-X[superscript 2] is a promising item-fit index for polytomous items in educational and psychological testing programs. Examples of the PARSCALE Codes Used for GPCM, PCM and RSM Calibration are appended. (Contains 4 tables and 1 figure.)
ACT, Inc. 500 ACT Drive, P.O. Box 168, Iowa City, IA 52243-0168. Tel: 319-337-1270; Web site:
Publication Type: Reports - Research
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: ACT, Inc.