Astronomy 141:
Life in the Universe Prof. Richard Pogge, MTWThF 12:30 |

A Worked Example

This example uses representative data from the Astronomy 161 class I taught Winter Quarter 2004, and is meant as a worked illustration of the grading process I follow for all of my introductory classes (Ast 161, 162, and 141).

Please keep in mind, however, that this is an **example** - every class
uses the same basic procedure, but are each a little different in detail
(e.g., number of exams/homework, relative weighting, etc.). Trying to using
the data here to estimate or predict your grade on your own will usually
lead to an erroneus or misleading result.

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. for each of the grade curves define the "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:

- I drop the worst of his four in-class exam scores. For Claude this
is Exam 1 where he got a grade-point score of 0.50 (D). The remaining
three in-class exams will each count for 15% of the final grade, or 45%
of the overall grade taken together.
- If there are extra credit points, they are applied to the score on
the
**Final Exam**. Thus, for example, if Claude had gone to the planetarium program and collected the extra credit point, I would have used a corrected Final exam score of (72+1)=73. Mr. Ptolemy didn't attend, so I will use the base score of 72. - I sum the scores from the 5 homework assignments (5 assignments of 5
questions each) and then curve that cumulative score to generate the
homework component of the grade. The homework counts for 15% of the
overall grade. Here, Claude got 18 of the 25 homework questions right,
which comes out to a grade-point equivalent of 2.81.
- I curve the final exam separately from the in-class exams and homework, and convert it into a grade-point equivalent. The final counts for 40% of the overall grade. Here, Claude got 72/100 on the final, which is equivalent to a grade-point score of 2.71.

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.

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Updated: 2012 February 9

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