ERIC Number: ED510479
Record Type: Non-Journal
Publication Date: 2007-Jun
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.
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.)
Descriptors: Item Response Theory, Models, Computer Software, Statistical Analysis, Goodness of Fit, Scores, Test Length, Sample Size, Educational Testing, Psychological Testing
ACT, Inc. 500 ACT Drive, P.O. Box 168, Iowa City, IA 52243-0168. Tel: 319-337-1270; Web site: http://www.act.org
Publication Type: Reports - Research
Education Level: N/A
Authoring Institution: ACT, Inc.