The process we're replicating:

• Exclude a column (don't include its grade in calculations at all).
• Drop the lowest grade.
• Add the remaining grades and divide by number of remaining grades.

What should be happening is:

Grade 1: 25
Grade 2: 100
Grade 3: 100
Grade 4: 100
Optional Grade 5: null (not included)

Drop 25, added 100+100+100. Divide the sum (300) by the number of columns (3) and get 100. This results in a percentage score of 100%.

Instead what appears to be happening is that it is dropping Grade 5 (the optional, excluded grade), adding 25+100+100+100, getting a sum of 325 and dividing that by 3. This results in a percentage score of 108.33%.

It knows the right number of columns to divide by (because we're dropping the lowest grade) but it's still including that lowest grade column in its math.

If we vary the column the lowest score appears in (e.g. moving Jane's lowest score to Grade #2) the problem remains.

If we change the value of the Grade to 50, the problem remains (but the percentage average is now 116.67%

I have attached two course backups to this tracker:

1. backup-ts101-20080109-1104.zip: An exact replica of the problem I describe.
2. backup-ts101-20080109-1146.zip: A modified version of the problem moving Jane's lowest grade to Assignment #2 and changing it's value to 50.

I've also uploaded an ODS export of the second example.

$grade = $grades_by_student["$exception->userid"]["$exception->catname"]["$assgn->name"]['grade'];
if (isset($grade)) {

if grade isn't set, and the lowest is set to be discounted, the user point total is kept but not the overall total. To fix it, we add this:

$grade = (empty($grade)) ? 0 : $grade;

We've tested it on two development instances, and it remedied the problem for us.

I got to the first student and became confused. There are obviously a 120 points; however, if we excluded one of those from the grading [because it is an optional assignment] then do we drop the lowest of the non-excluded grades? If so the total would be 115 points and not a 120 and the possible points would be 135 since the excluded was optional. So I would say that the first students grade shoulld be 115/135.

Student2 (Charlie) never turned in the "optional" assignment (A5) so it is ungraded; however, he is not excluded from it (for whatever reason). So he has 200 possible points and then we remove the lowest grade which is A5. So Charlies has 125 of the possible 150 points - 125/150.

The third student, third assignment poses an interesting scenario for dropping the lowest and demonstrates the issue with lowest percentage or lowest points. If you drop the lowest points you will be dropping an assignment the student scored 100% on. I would student 3 should be 170/175.

Student4 (Gabiel) - Did the optional assignment (A5) so poorly as to merit a grade of zero. Gabiel also earned a zero on A4. Which assignment do we drop? If you drop A5 then Gabiel has 20/150; however if A4 it is 20/100. I would say we ought to drop the one worth the most points which is A4. So Gabiel would have 20/100.

Student5 (Ignacio) - Was not required to do A5 so it is excluded. Then we drop the lowest grade (A4 or A3? - one is zero and one is blank, again I say the one worth the most points so A4). So I think Ignacio's grade would be 25/50.

Let me know your thoughts on this data.

Peace - Anthony

http://www.jesuitscholar.com/MDL12842

http://www.jesuitscholar.com/MDL12842P

Using that data, let's see if we agree on the desired results.

Student1 - 115/135 (exclude #5, drop #2) - straight forward, exclude #5, drop lowest #2
Student2 - 125/150 (exclude nothing, drop #5) - drop #5 since it is null = 0 and not excluded
Student3 - 170/175 (exclude nothing, drop #3) - drop #3 because percentage is lower than #1
Student4 - 20/100 (exclude nothing, drop #4) - percentage is the same (4 and 5) but impact on grade is higher
Student5 - 25/50 (exclude 5, drop #4) - percentage is the same(3 and 4) but impact on grade is higher

I suspect that this will take a major overhaul of the function used to calculate the grades. Before I dive into I want to make sure we agree on the goal.

Peace - Anthony

For each category
For each grade_item
if excluded item (do not add to points and possible points)
otherwise keep a running total of points and possible points
Sort grade_item array by percentage (ASC) and possible points (DESC) so we know which ones count more
For however items are to be dropped subtract points and possible points from running totals

In that way excluded grades are never included and then dropped grades are taken out based on the lowest percentage, max points.

Does that make sense?

To piggyback on your comment, in addition to those grades/max scores, we expect these percentages:

115/135 85.18
125/150 83.33
170/175 97.14
20/100 20.00
25/50 50.00

Based on the logic you've outlined, these numbers are what you'd expect to see.

As far as the preference goes as to which to discard (greater impact on grade or lower impact on grade) I can see people arguing it both ways; if you go with the later though, you're effectively discarding tests in favor of quizzes, right?

I'll bounce it off my instructional technologists tomorrow and see if they have any practical use cases that might inform this. Whatever way this goes though, I think we need to update the documentation to spell out what the logic is here; that the preferred approach is not to have grades of differing max scores, and that if you do use differing values, be aware that the X is dropped in favor of Y because of Z.

As for the patch, I concur; it is not fixing the problem; we can confirm this by matching the actual percentages with the expected ones above.

For this course, we have a total possible score (assuming the student completed all assignments) of 200.

For Student #1 (Baker, Adam), Assignment #5 is excluded. This drops his total possible score to 150. His cumulative grade, without dropping the lowest score, is 120 out of 150.

We drop his lowest grade, which assuming we're using percentages to calculate lowest grade, should be Assignment #2 (5/15). This lowers his total possible score to 135. His cumulative grade, dropping the lowest percentage score, is 115 out of 135. This should out to 85.14%.

What the patched version appears to be doing is using Assignment #2 (5/15) as the lowest grade (giving us 5) but Assignment #1 (10/10) as the lowest possible score (give us a 10).

The hidden math is a cumulative grade of 115, but a total possible score of 140. 115/140 gives us 82.14%, which is the value we see on screen.

This did not show up in my version, because all the assignments were worth the same amount of points (100) so it didn't matter which assignment it considered to have the lowest possible max score.

if ($main_category['stats']['drop'] != 0) { // I think the exceptions should be handled not only first but separtely from drops

Later when re-calculating after removing excluded and dropped grades the logic begins with:

if (isset($exceptions) && $exceptions) {

and then handles the drop cases within that if statement.

I'm going to need to print out the function and do some major refactoring. If I can get away with a minor fix I will; however, I am going to do so with great care which means I will need more time. It may well be June before I really get a chance to work on this again.

If someone is able to provide a patch before then I would be happy to look at it. I've got some good notes which should help me along when I do get back to it but I wanted to let you know that it may be a while.

Peace - Anthony