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Stout, William F. Li, Hsin-Hung 2011-05-07T13:53:52Z 2011-05-07T13:53:52Z 10000-01-01 1995 Unidimensionality is one of the most important assumptions required by much of the currently used item response theory (IRT) methodologies. In the first part of this thesis, a further and non-trivial practical refinement of DIMTEST(Stout, 1987; Nandakumar & Stout, 1993) is made to assess latent trait unidimensionality for mixed dichotomous and polytomous items. The modification is referred to Poly-DIMTEST. The new test statistic for polytomous item scoring was carefully developed and defended with an appropriate asymptotic theory. A simulation study then was carried out to investigate the performance of Poly-DIMTEST. The results demonstrate that Poly-DIMTEST has good Type I error as well as good power. We conclude that the Poly-DIMTEST procedure shows promise as a useful tool in assessing unidimensionality for mixed dichotomous and polytomous test data. The purpose of the second part of this thesis is to present a hypothesis testing and estimation procedure, Crossing SIBTEST, for detecting crossing DIF. Crossing DIF exists when the difference in the probabilities of a correct answer for the two examinee groups changes signs as ability level is varied. In item response theory terms, crossing DIF is indicated by two crossing item characteristic curves. Our new procedure, denoted as Crossing SIBTEST, first estimates the matching subtest score at which crossing occurs using least squares regression analysis. A Crossing SIBTEST statistic then is used to test the hypothesis of crossing DIF. The performance of Crossing SIBTEST is evaluated in this study. Made available in DSpace on 2011-05-07T13:53:52Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9543649.pdf: 3595450 bytes, checksum: 19e38440cac1ee52a0555b0295f6275b (MD5) Previous issue date: 1995 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T15:00:30Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:28:37-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission ETDs are only available to UIUC Users without author permission U of I Only AAI9543649 (UMI)AAI9543649 http://hdl.handle.net/2142/22859 eng Copyright 1995 Li, Hsin-Hung Education, Tests and Measurements Statistics Psychology, Psychometrics New nonparametric statistical procedures for analyzing bias/DIF and dimensionality in item response data text Statistics Statistics University of Illinois at Urbana-Champaign Dissertation Ph.D.