Using adjusted GPA and adjusted course difficulty measures to evaluate differential grading practices in college

In this study, the Rasch rating scale model (Andrich, 1978) was applied to college grades of four freshman cohorts from a large public university. After editing, the data represented approximately 34,000 students, 1,700 courses and 119 departments. The rating scale model analysis yielded measures of student achievement and course difficulty. Indices of the difficulty of academic departments were derived through secondary analyses of course difficulty measures. Differences between rating scale model measures and simple grade averages were examined for both students, courses, and academic departments. The differences were provocative and suggest that the rating scale model could be a useful tool in addressing a variety of issues that concern college administrators.