Students’ preference for grading rules: The role of ratio bias

Ratio bias exists if people perceive the likelihood of an event to be greater when it is presented as a ratio with large numbers (e.g., 10 in 100) than when it is presented as a ratio with small numbers (e.g., 1 in 10). This study shows the prevalence of ratio bias by examining students’ preference for grading rules at a college that uses a relative grading system. The study was conducted in an institution allowing instructors who teach multiple classes of the same course to grade students as if they are enrolled in a single class by pooling students of different classes (pooled grading, or PG). The other (default) alternative was to grade students separately based on each class (separate grading, or SG). We find that students strongly prefer PG to SG, which indicates that students’ preferences are affected by ratio bias. We also find that preference for PG is not affected by gender, but older students are less likely to choose PG than younger ones. Lastly, by conducting an additional experiment, we confirmed that students’ preference for grading rules in the original survey is not likely to be affected by overconfidence or social bias, nor could it be affected by the type of questionnaires.