Sunday, May 24, 2009

Grading On a Curve Sucks

Grading on a curve sucks -- there, I said it. For some reason whenever I teach statistics I get quasi-joking comments about "do I grade to a bell-curve", at which point my response is a rather intense diatribe against the very notion. To my perspective, mashing data (grades which are not normally-distributed) to some desired different outcome (the normal bell curve) is simply outright fraudulent, and demonstrates a complete lack of understanding of statistical analysis, or what the normal curve should be used for as an analysis tool.

Back in Fall 2006 Thought & Action magazine published an article by Richard W. Francis (Professor Emeritus in Kinesiology, California State Fresno), asserting that grading on a curve is the only way to properly compute grades (titled in a propagandist fashion, "Common Errors in Calculating Final Grades"). Here's my letter to the editor from that time:

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Dear Editor,

Richard W. Francis proposes a system for standardizing class grading (Thought and Action, Fall 2006, "Common Errors in Calculating Final Grades"). The system takes as its priority the relative class ranking of students, even though I've never seen that utilized for any purpose in any class I've been involved with.

Mr. Francis responds to some criticism of his system effectively grading on a curve. His response is that instructors can "use good judgment and the option to draw the cutoff point for each grade level, as they deem appropriate". In other words, after numbers are crunched at the end of the term, the grade awarded is based on a final, subjective decision by the instructor. Moreover, there is no way to tell students clearly at the start of the term what is required of them to achieve an "A", or any other grade, in the course.

The example presented in the article of a problem in test weighting seems unpersuasive. We are presented with a midterm (100 points, student performance drops off by 10 points each), and a final exam (200 points, student performance drops off by 5 points each). It is presented as an "error" that the class ranking matches the midterm results. But since the relative difference in the midterm is so large (10% difference each step) and the final so small (2.5% difference each step; even scaled double-weight that's only 5% per step) this seems to me like a fair end result.

Take student A in the example, who receives an "A" on the midterm and a "C+" on the final (by the most common letter grade system). In the "erroneous" weighting he receives a final grade of "B", while in the standardized system he has the T-score for a "D+". Clearly the former is the more legitimate reflection of his overall performance.

As an aside, I have a close relation who was denied an "A" grade in professional school due to an instructor grading on the curve. He still complains bitterly about the effect of this one grade on his schooling, now 40 years after the fact. Any subjective or curve-based system for awarding student grades at the end of a term damages the public esteem for our profession.

Daniel R. Collins
Adjunct Lecturer
Kingsborough Community College

2 comments:

  1. I don't understand something: how the heck can someone who gets an A and a C+ as contributing grades, end up with a D+?! No matter what weights you'd assign to the grades, the final result must be between and including C+ and A.

    It's a wholly separate issue that IMHO grading on the curve is a thoroughly idiotic thing to do. Grade, as a measure of some sort of academic achievment, is isolated from what others do. Surely a teacher may be bad, or co-students may be influencing you negatively, and life is generally unfair, but that doesn't mean that you magically achieved more just because the conditions were poor. Nobody adjusts athletic scores in paralympics just because the competitors are at some disadvantage compared to those who have full use of their body. Similarly, a grade should tell you how well you did, on an absolute scale of some sort. If everyone in the class did poorly, that doesn't mean there should be a couple A's awarded just for trying hard. Grades shouldn't measure effort or anything of the sort, IMHO. They should measure the mastery of the subject matter. For some it will come easy, for some it will come hard, oh well.

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    1. Well, of course I completely agree with you. But apparently in some places people think that the most fundamental use of grading is as a measure of relative standing, i.e., who's ahead of who (unrelated to satisfying any particular objective skill level). Seems insane to me, but I can dig up lots of examples of people arguing that way.

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