Assessing Impact, DIF, and DFF in Accommodated Item Scores: A Comparison of Multilevel Measurement Model Parameterizations

This pedagogical article is intended to explain the similarities and differences between the parameterizations of two multilevel measurement model (MMM) frameworks. The conventional two-level MMM that includes item indicators and models item scores (Level 1) clustered within examinees (Level 2) and the two-level cross-classified MMM (in which item scores are cross-classified by two Level 2 classifications including item and examinee) are discussed. A small subset of National Assessment of Educational Progress 4th grade mathematics item scores is used to demonstrate use of the MMMs for assessing facets of the validity of accommodated test scores. The models' similarities and distinctions are emphasized as well as the flexibility of the models' extensions.