Effects of Anchor Item Choices on Bias on the Force Concept Inventory across the intersection of gender and race

Education researchers often compare performance across race and gender on research-based assessments of physics knowledge to investigate the impacts of racism and sexism on physics student learning. These investigations' claims rely on research-based assessments providing reliable, unbiased measures of student knowledge across social identity groups. We used item response theory (IRT) and differential item functioning (DIF) analysis to examine whether the items on the Force Concept Inventory provided unbiased data across social identifiers for race, gender, and their intersections. A crucial choice in any IRT/DIF analysis is what items to "anchor" across groups, that is, which items are assumed to behave the same. Here we discuss how the choice of anchors significantly alters the results of any such analysis, the assumptions each choice of anchors carries with it, and how these choices affect the interpretation of the results.