Differential item functioning analysis reveals equitable confidence development in undergraduate field courses

Assessing whether instructional approaches produce equitable outcomes requires attention to both what we measure and how we measure it. We applied differential item functioning (DIF) analysis to examine equity in how field-based learning shapes students' confidence in their scientific skills across three undergraduate biology courses. Following a theory-based approach to DIF, we generated predictions grounded in prior evidence that field biology courses may help close confidence gaps between demographically dominant and nondominant students. Our demographic DIF analysis revealed that items generally functioned equivalently across demographic groups within field courses, indicating equitable skills-based confidence development for first-generation and low-income students. For underrepresented minority (URM) students, we observed a gap-closing trajectory in which students who entered with lower confidence showed greater positive change than their non-URM peers at equivalent overall confidence levels. Our course DIF analysis provided confirmatory evidence that substantial response differences emerged between field and lecture courses, with the strongest patterns on items most closely tied to field-based activities. Students in the introductory field course were 2-34 times more likely to give higher ratings than lecture course students at equivalent overall confidence levels, while students in the intensive field course showed even stronger patterns (8-167 times more likely). These findings demonstrate that field-based learning builds students' confidence in ways that are equitable across diverse populations and may help close confidence gaps for historically minoritized students.