Posts Tagged 'grading'

Missing the Important Stuff

Bear with me as I force an analogy between watching basketball and grading physics quizzes.

When I watch basketball on TV, especially during March Madness, I’m often annoyed by the way they handle the replays.  After an exciting play, I’ll yell at the TV, begging for a replay so that I can see again exactly how the play developed.  When they do show the replay, I’ll often end up yelling at the TV again, because they left out all the important part of the play.

They show the shot being released, traveling through the air and splashing through the net, ignoring the pick and roll and the deft pass that set up the shot.  The time that the ball is in the air is really the least interesting part of that play.  The ball flies the same way every time, and we already know the result of the play.  Show us how they got there.

Or they show the dunk at the end of a fast break, hiding the defense that set up the break and the smart decicion making of the point guard that got the ball to the right player to finish the play.  The dunk gets the fans excited and shows up on Sports Center, but it doesn’t happen without the key plays that set it up.

Now the switch to physics…

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More on Exam Grading

Well, I should be studying for my last final, so of course, I’ve been reading blogs and watching the snow fall while searching for the right Christmas music station on Pandora.  (The Vince Guarladi Trio, of Charlie Brown fame, should work nicely for studying, while not bringing up any Bing Crosby or Perry Como to drive me nuts.)

So, since I’m being so productive anyway, I thought I’d share a few more thoughts on grading and curving that have come to mind since reading the comments on the last post

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Creative Exam Curving

Well, it’s Final Exam week for me, so tests have naturally been on my mind.  In teaching undergrads, (especially pre-med students), I’ve gotten many anxious questions about exam grading and how the exams might be curved.  While I have no control about how grades are curved or scaled for my students, I’ve been thinking about the many different ways to accomplish this task, both traditional, and some more off-the-wall ideas that I’ve had.
First, the traditional ones:

What You See is What You Get

The scale is set ahead of time, and the percentage of the points that you get is your score, plain and simple, no haggling.  While this seems to leave no wiggle room for the grader, the grader will no doubt consciously unconsciously scale the grades as he goes along, particularly if there’s partial credit to be awarded (and there almost always is).  In addition, the grader may find himself choosing the letter grade that the solution deserves, and then adjusting the points to fit that grade.

Normalizing to Unity

Take the highest score, and add the necessary points to get it to 100%.  Then add the same number of points to everyone else’s score.  Really, to make it a true normalization process, you should divide all scores by the highest score to get the new percentage, but adding points is more beneficial to the students, and is what is usually done.  The good thing about this is it has some ring of fairness to it — students can’t complain about unfairness, because at least one student got an A.

However, this approach can lead to civil unrest in the case of a “curve-breaker,” a student who scores significantly higher than the rest of the class, thus reducing the benefit of the curve.  There are ways around this: either curve the outlier’s score above 100, or, if that offends you, just give that student less of a curve than anyone else.  If they complain about getting “only” 100%, then tough noogies.

Normalizing the Average

Instead of rescaling the top score, rescale the average score to whatever you’ve decided the average grade to be, usually a B or a C.  This can again be accomplished by either addition or multiplication, and faces the same potential problem of putting students above 100%.  Also, what if the students score better than expected?  Are you really going to scale them down to a C?

The Good ‘Ol Bell Curve

Find the average, find the standard deviation.  Everybody within one sigma is a C.  Two sigma is a B or a D, beyond that is an A or an F, where appropriate.  I don’t know if this is really done much, and I always thought it was unfair, but I was in a class where the Central Limit Theorem really applied.  However, in a huge state school like mine, scores might actually approach a normal distribution in the large lecture classes.

But do we really want to give 68% of our students a grade of C?  I don’t think C means average to most people anymore, so if you were to use this one, you probably would want to make the average correspond to a different grade.

And now, for some more creative ideas….

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