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Chen, Hanwei; Cui, Zhongmin; Zhu, Rongchun; Gao, Xiaohong – ACT, Inc., 2010
The most critical feature of a common-item nonequivalent groups equating design is that the average score difference between the new and old groups can be accurately decomposed into a group ability difference and a form difficulty difference. Two widely used observed-score linear equating methods, the Tucker and the Levine observed-score methods,…
Descriptors: Equated Scores, Groups, Ability Grouping, Difficulty Level
Kang, Taehoon; Petersen, Nancy S. – ACT, Inc., 2009
This paper compares three methods of item calibration--concurrent calibration, separate calibration with linking, and fixed item parameter calibration--that are frequently used for linking item parameters to a base scale. Concurrent and separate calibrations were implemented using BILOG-MG. The Stocking and Lord (1983) characteristic curve method…
Descriptors: Standards, Testing Programs, Test Items, Statistical Distributions