As is apparent, controlling for the distribution of classes substantially reduces the residual increase in grades. Hence, changes in the distribution of classes have contributed about 0.1 grade points to average GPAs over the 20-year period. Adding controls for demographics reduces the residual grade inflation by roughly another 0.1 grade points. In short, after controlling for both course selection and the characteristics of students, the average increase in grades is roughly half the unconditional increase. Figure 2 examines how the distribution of grades changed between the beginning and ending of the sample period using the reweighting technique detailed above. The dark blue bars illustrate that in 1982 about 24 percent of grades were As, 35 percent Bs, 27 percent Cs, 9 percent Ds, and 4 percent Fs. By 2001—the green bars in the chart—the proportion of As had increased to 38 percent and Bs, Cs, and Ds, had fallen to 34 percent, 18 percent, and 6 percent; Fs were about unchanged. Reweighting the 1982 data to match the student characteristics and course enrollment patterns of 2001 (the light blue bars) suggests that a substantial portion of the increase in grades is accounted for by changes in observable characteristics. For instance, according to this analysis about 30 percent of students in 1982 would have received As if they had the SAT scores and other characteristics of students in 2001 and if they had the same enrollment patterns as did students in 2001. In this counterfactual, 30 percent of 1982 students would have received As, 37 percent Bs, 23 percent Cs, 7 percent Ds, and 3 percent Fs. Overall, in this analysis, changes in characteristics and course choices account for a bit more than half of the increase in average grades over time, and for slightly less than half of the increase in the proportion of students receiving As. Figure 2: Changes in the Distribution of GradesNote: Figure illustrates the distribution of actual course grades assigned in 1982 (dark blue) and in 2001 (green). The light blue bar represents actual grades assigned in 1982 reweighted to represent the demographic characteristics, SAT scores, and department and course selections of the actual 2001 students. Discussion
Appendix 2: Selected additional course match examples 1985 Course 2001 Course Accounting 405: Corporate Taxation Tax planning and research. Income taxation with emphasis on special problems applicable to corporations, partnerships, estates, and trusts. Preq: Junior standing. Accounting 406: Business Taxation Provides an introduction to the importance of taxation in business decision making; emphasizes the interrelationship of taxes, the choice of business form, and various business transactions; exposes students to the breadth of business decisions which are affected by the Federal Income Tax. Preq: A grade of C or better in ACCT 301. Computer Science 120: Introduction to Information Processing Systems Introduction to the techniques, principles and concepts of modern information processing systems, intended primarily for nontechnical majors. Topics include information processing packages and application, usage of typical information processing packages, digital computers, programming fundamentals and languages, and implementation of computer programs. Computer Science 120: Introduction to Information Technology Investigation of ethical and societal issues based on the expanding integration of computers into our everyday lives. Historical background, terminology, new technologies and the projected future of computers are considered. Practical experience with common computer software technologies is included. Will not satisfy computer science requirements in any computer science major. Political Science 422: Public Policy Analysis Selected views of public administration and the problems involved. Preq: POSC 101 or consent of instructor. Political Science 421: Public Policy Processes Introduction to public policy process, analysis, and evaluation. Topics include examination and comparison of policymaking models, policy analysis and decision-making techniques, and approaches to program evaluation. Preq: PO SC 101, Junior standing, or consent of instructor. Zoology 201: Invertebrate Zoology A survey of the phyla of invertebrate animals, including their taxonomy, morphology, development, and evolution. Preq: BIOL 111 or consent of instructor. Biological Sciences 302: Invertebrate Biology In-depth survey and comparison of free-living invertebrate animals emphasizing functional anatomy, development, and evolutionary relationships. Preq: Introductory two-semester biology sequence with laboratory. Coreq: BIOSC 306. Appendix 3: Comparison of Full Sample with Regression Sample The raw data we received from the university contains about 3.1 million course observations. From the outset, we drop the roughly 400,000 observations of graduate courses, which are those