Statistics work only if I have a reference point

[trinityvixen]

So I did poorly on a chemistry test this week. I'm not fussed about it for a number of reasons--I've done well on other tests, this is a course I'm not sure I need, I've already taken it so I'm not concerned about knowledge I don't have. What I am is confused. I figured I'd throw this out to the people I know who know stats better than I ever have, do, or will.

Our grades are computed based on "z-scores," as befits a curve (apparently) that takes into account the fact we can drop one grade. This score equals [my score]-[test average]/standard deviation. The average z-scores of the class are then ranked. This is all well and good, but what rank/score equals what grade is not specifically ever stated. They say they chart the z-score averages, presumably on a histogram, and wherever there is a "break" in the graph--meaning a significant drop in the numbers of people at a given average z-score--there will be a change in letter grade. But since you have no idea where those breaks will be until all the tests are counted, including the final...what the hell will your grade be?

This is a useless way of keeping track of how well I'm doing. Also, pardon me and my non-statistical thinking here, but how does grading people based on how much better/worse they are than their peers accurately value what they've learned? This is not a new problem I know--this is the curse of the curve--but still!

Comments

[chuckro.livejournal.com]

The only real value to a curve is offsetting the professor's inability to teach/write a good test. Grades are only useful as a relative score (you versus other students) if they were first an absolute score (how much of the material you know) which means that the only thing grade deflation does is hurt students when they are then compared again other departments and schools.

If they really wanted to make grades useflu as an arbitrary measure, they'd need to give both an "absolute" score of how much of the subject you knew, based an a standardized exam, and a "relative" score versus your class and previous classes by the same professor. But that would be much harder to turn into a GPA that idiot recruiters could put in a spreadsheet and sort by.

[trinityvixen.livejournal.com]

I think you've got a pretty fair system. This is an intro course; the material is probably fixed and the teachers rotate. It should be pretty easy to generate a standardized score and then apply it against the scores in class.

Man, whatever happened to just "If you score this, it is an A"? I knew where I was with that scale.