A tutorial on item response modeling with multiple groups using TAM

Multiple-group item response theory (MGIRT) is the standard psychometric model for the analysis of large-scale assessments in education. In this tutorial, a short nontechnical introduction to MGIRT is first provided. Second, the R package TAM and the included relevant functions to estimate MGIRT are introduced and applied to a small data set from the science assessment of TIMSS 2019 for Grade 8. Specifically, the following techniques are illustrated: the estimation of population parameters, analysis of differential item functioning (DIF; also referred to as non-invariance), and linking under full non-invariance. The hands-on training in this walkthrough enables researchers to estimate MGIRT with TAM and interpret the outputs confidently.