The thing that bothers me about systems like this is that it seems to give legitimacy to the totally arbitrary scale that says "90% is an A." There is no legitimacy to such a scale. I'm not picking on Mark here, but I want to point out that we SHOULD find his statement to be totally meaningless! Again, this is not a dig at Mark. It's a dig at the fact that we all understand exactly what he means!
After his formula, he said, "Hence an 80 becomes about a 90; a 50 becomes about a 70; a 100 stays at 100."
We all know that 90 means "bottom of the A range" and 70 means "bottom of the C range." But why? What is so magical about those cutoffs? They are completely arbitrary. Percent means nothing without "of _____." But we treat 90% as if it has meaning.
What Mark said should be meaningless. We've turned one set of numbers into another set of numbers. Why is that second set any better for purposes of assigning grades? I would much rather look at the quality of work on the test and make grade decisions based on that. If a test is more difficult I'll use a different set of cut scores than I would on an easier test.
Converting things to the 90-80-70-60 scale does two things: 1. It removes the responsibility from us for assessing the quality of the work. 2. It reinforces the idea that the arbitrary grading scale is in some way valid, and is therefor dishonest.
When I assign grades I look for clusters that appear in the distribution. Then I skim a few of the papers in each cluster and decide if they look like A work, B work, etc. Sort of akin to "Complete Response, Developing Response," etc. The better scores in a cluster may get a 'plus' and the worse ones a 'minus.'
I enter the letter grades into my grading program and it assigns a number for calculation purposes, but it is not based on a percent of anything.
Now I'll step off my soapbox.
________________________________________ From: Dennis Roberts [email@example.com] Sent: Wednesday, May 30, 2012 8:33 PM To: AP Statistics Cc: AP Statistics Subject: Re: [ap-stat] Final Grading
At 11:20 AM 5/30/2012, Mark Marstaller wrote: >Our chemistry teacher uses a 10 * SQRT(Raw Score) for hers--you can >modify for your needs. Hence an 80 becomes about a 90; a 50 becomes >about a 70; a 100 stays at 100. You could use a different multiplier.
I am sure there is some psychometric logic to this .. >:-}