What Are Grades Made Of?

The term "grade inflation" covers a multitude of phenomena, some of which are even alleged to be sins. Continuing increases in average grades have been widely documented in many universities over the last several decades. Also widely documented, and often associated with grade inflation, are systematic differences in grade levels by field of study, with a common belief that the sciences and math grade harder than the social sciences, which in turn grade harder than the humanities -- and that economics behaves more like the natural sciences than like the social sciences. The general persistence of these relative differences in grades seem to us to be more interesting and more difficult to explain than the persistence of modest grade inflation in general, and they are the principal focus of this paper. Why, for example, should average grades in English be much higher than average grades in chemistry? And what is going on when relative grades change, when a department's grading practices change markedly relative to other departments? We explore such questions using detailed data on grades at the University of Michigan from Fall 1992 through Winter 2008.