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Differential item functioning analysis using a multilevel Rasch mixture model: investigating the impact of disability status and receipt of testing accommodations.

The assessment of differential item functioning (DIF) remains an area of active research in psychometrics and educational measurement. In recent years, methodological innovations involving mixture Rasch models have provided researchers with an additional set of tools for more deeply understanding the root causes of DIF, while at the same time increased interest in the role of disabilities and accommodations has also made itself felt in the measurement community. The current study furthered work in both areas by using the newly described multilevel mixture Rasch model to investigate the presence of DIF associated with disability and accommodation status at both examinee and school levels for a 3rd grade language assessment. Results of the study found that indeed DIF was present at both levels of analysis, and that it was associated with the presence of disabilities and the receipt of accommodations. Implications of these results for both practitioners and researchers are discussed.