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ERIC Number: ED481656
Record Type: Non-Journal
Publication Date: 2003-Apr
Pages: 20
Abstractor: N/A
Reference Count: N/A
Impact of Item Drift with Non-Normal Distributions.
Witt, Elizabeth A.; Stahl, John A.; Bergstrom, Betty A.; Muckle, Tim
The focus of this simulation study was to investigate the effects of item difficulty drift on the stability of test taker ability estimates and pass/fail status under the Rasch model. Real, non-normal distributions of test taker abilities and item difficulties were used to represent true parameters. Test taker responses for 18 conditions of item drift were simulated; ability estimates were obtained using the WINSTEPS program (J. Linacre, 1999) and compared with baseline data. Results are encouraging in that they provide further evidence of the robustness of Rasch model ability estimates in the face of undetected item drift. A fairly large number of item difficulties (e.g. 25%) must be altered before even a hint of possible distortion of ability estimates appears. (Contains 7 tables and 12 references.) (SLD)
Publication Type: Reports - Research; Speeches/Meeting Papers
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A