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
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
Why%20Have%20Undergraduate%20Grades%20Increased%202.27.13.docx