You try to fit the marks to a normal distribution. It assumes that all classes/courses have the same distribution, with the same midpoint and that the only variation is that the test was too easy.
So, (simplistically) if the expected midpoint is 75, and everyone is in the 95-100 range, a grade of 97.5 would be shifted down to 75.
It does penalize students for having really smart friends and getting together to take a difficult course.
So, (simplistically) if the expected midpoint is 75, and everyone is in the 95-100 range, a grade of 97.5 would be shifted down to 75.
It does penalize students for having really smart friends and getting together to take a difficult course.
http://en.wikipedia.org/wiki/Grading_on_a_curve