I did some tests on gradebook_cdc version currently in CVS and ran into some problems when some students didn't get any grade in a category
I created a test course with 4 students and only 2 assignments (A1 and A2)
Statistics give the following results:
We se that even in this simple case where everybody has at least a grade some results are wrong, median in my opinion should be (20+24)/2 (but I agree that some authors may accept 20 or 24 !) and stddev should be 4.87 not 6.88 (no discussion on this one !)
Now I add a 5th student with no grade
It's a little annoying for me that total for BB Wolf display 0, I would expect it to be '-'
Statistics results are now :
So Now Median is really wrong (considering 0 grade only make it worst) average is right if you consider 0 grade (but wrong in my opinion because Wolf has no grade so should not be taken into account). And stddev is very far from the real value (it should be 10.09 if you take 0 grade into account and 4.87 if you don't)