This is probably something simple or statistical that I am missing? Is it ratio?
It may be some sort of regression co-efficient. Other quiz analysis systems use a statistic that is basically "is there a good correlation between the students' score on this question, and their score on the whole quiz?" If there is a good correlation, then that question is probably a good indicator of ability.
By the way, have you tried clickin on the help buttons or looking in MoodleDocs?
Discrimination Coefficient means Corrected Item-Total Correlation or not?
DC = Sum(xy)/ (N * sx * sy)
Some statistical packages, like SPSS, use overall quiz scores decremented by score for that particular queastion i.e. C = Y - X
I don't think it is corrected. It does not mention that in the documentation.
When all the students get a question correct, and so I guess that the discrimination coefficient should be 0 (zero) because it has no power of discrimination but it is also not reverse discriminating, but in moodle 1.53 it is calculated to be 999.
Someone in a training session I was conducting at my school said "Raw."
Whether this is correct or not, I'm not sure. But, it works. "Raw Count." "Raw %."
Thought I should share.