Introduction to Stars, Galaxies, & the Universe
Prof. Richard Pogge, MTWThF 9:30
This example uses representative data from Astronomy 161 during Autumn Quarter 2005, and meant is meant only as a worked illustration of the grading process. Using the data here to try to estimate your grade on your own could result in an erroneus or misleading result. Examples of extra credit are just that, examples, not indications of what I will (or won't) regard as extra credit during a given quarter. For that information, see the syllabus.
I compute your overall course grade by converting the scores on the exams and the homework into a grade-point score on the OSU 4-point grading scale, and then combining these grade-point scores to compute the final grade and generate a letter grade.
The divisions between A, B, C, etc. given for each of the exam grade curves define the various "break points" of the conversion. Note that this is not a simple percentage conversion (for example, I do not use 90%=A, 80%=B and so forth), nor is the conversion between a test score and a grade-point score a simple formula (I have to do a numerical interpolation on the break points, but that's a computational detail).
Homeworks are slightly different in that I first add up all of the scores for the 5 homeworks, and then create a curve for the total to use to convert total score into a grade-point equivalent. Because there are only 5 questions, it is pointless to try to curve each homework assignment.
The 4-point grading scale is defined in terms of the lowest grade-point score (GP) that is assigned to each letter grade:
GP Letter 3.85 A 3.50 A- 3.15 B+ 2.85 B 2.50 B- 2.15 C+ 1.85 C 1.50 C- 1.15 D+ 0.50 DThe way to read this table is as follows: in order for person to get a B+, their grade-point score must be at least bigger than 3.15, and below 3.50. Note that OSU does not give D- or F grades, but does give grade-point scores below 0.50 an "E".
To illustrate how a grade is computed in detail, I've created a fictitious student, Claude Ptolemy, who got the following test scores this quarter. The grade-point scores were computed using the grade curves for the various exams and the cumulative homework assignments.
raw % score score GP Letter ---------------------------------- Exam1 23/50 46% 0.50 D Exam2 31/50 62% 1.93 C Exam3 29/50 58% 1.64 C- Exam4 32/50 64% 2.07 C Homework 18/25 72% 2.81 B- Final 72/100 72% 2.71 B- -----------------------------------
In computing Claude's overall grade, I do the following:
Once this is done, the final grade is computed by combining each of the three pieces. For Claude, this looks like this:
Overall = 0.15*Exam2 + 0.15*Exam3 + 0.15*Exam4 + 0.15*Homework + 0.4*Final = (0.15*1.93) + (0.15*1.64) + (0.15*2.07) + (0.15*2.81) + (0.4*2.71) = 0.290 + 0.246 + 0.311 + 0.422 + 1.084 = 2.352In this example Claude has an overall grade-point score of 2.35 for the class. On the OSU 4-point scale, the lowest grade-point score that gets a C+ is 2.15, and the lowest score that gets a B- is 2.50. Since 2.35 is between 2.15 and 2.50, Claude will get a grade of C+ for the class.