PARA Accessible Reading Assessment Reports: Examining DIF, DDF, and Omit Rate by Discrete Disability Categories

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A report describing a study of differential item functioning (DIF), differential distractor functioning (DDF), and differential omission frequency (DOF) for one third grade and one fifth grade statewide reading test for three disability groupings: students with speech/language impairments, learning disabilities, and emotional/behavioral disorders. The study found substantive DIF/DDF only for students with learning disabilities, not for students with speech/language impairments or emotional/behavioral disorders. Furthermore, examination of response characteristic curve graphs showed that DIF/DDF did not necessarily indicate an item had statistical bias against students with learning disabilities. Rather, low-performing students with learning disabilities more often than low-performing students without disabilities appeared to choose wrong answers randomly rather than selecting the most appealing wrong answers. The researchers concluded that there was no evidence of test bias for students with disabilities in the state reading tests examined in the study.

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