Gradebook: Unexpected behavior in selection of lowest grade to drop and resultant category calculation

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Details

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 1.9, 1.9.12
• Fix Version/s:
• Component/s:
• Labels:
• Database:
Any
• Testing Instructions:
Hide

delete all gradeable activities (or create a new course)
create 3 assignments. use "simple direct grading". Set them to have a maximum grade of 5, 10 and 15 respectively.

You may want to keep the grader report and categories and items "full view" open in 2 tabs.

Go to the categories and items "full view" screen.
Click the edit/hand icon for the course grade item.
Set aggregation to "simple weighted mean of grades".
Go to the grader report and enter a grade of 10 for the assignment out of 10

On the categories screen, set "drop the lowest" to None.
On the grader report, the students course grade should become 100% --> (1.0*10)/10
1.0 = the student grade, 100%
the first 10 = the assignment maximum
the other 10 = the sum of all included activity maximums
(The student only has a single graded and they got 100% so their course grade is 100%)

Untick "Aggregate only non-empty grades" for the course
Course grade should become 33.33%--> (0.0*5 + 1.0*10 + 0.0*15)/30
(the other assignments are now included and are counted as 0)

On the categories screen, set "drop the lowest" to 1.
Course grade should become 66.7% (or 66.67 or similar) --> (0.0*5 + 1.0*10)/15
(the denominator was reduced due to the removal of the assignment out of 15, the most "weighty" assignment)

Enter a 0 for the assignment out of 15.
Course grade should stay at 66.67 --> (0.0*5 + 1.0*10)/15
(it makes no difference if the assignment grade is 0 or empty)

Enter a 0 for the assignment out of 5.
The course grade should stay the same.

Un-override the assignment out of 15 (it goes back to being empty)
The course grade should stay the same.

Un-override the assignment out of 5.
The course grade should stay the same.

Un-override the assignment out of 10.
The course grade should go back to 0.

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• Affected Branches:
MOODLE_19_STABLE
• Fixed Branches:
MOODLE_22_STABLE, MOODLE_23_STABLE
• Pull from Repository:
• Pull Master Branch:
MDL-13629_droplow
• Pull Master Diff URL:

Description

Using simple weighted mean of grade with assignments of varying point values I am not sure what the logic ought to be for selecting the lowest grade. I would assume that it would be the lowest percentage (points earned/points possible) for an assignment and where there are multiple zeros that it would select the one with the highest possible points (i.e. the one that would have the greatest weight).

I would expect a blank and zero to be treated the same unless the gradebook as been set to ignore blank grades. In my particular case, I did not check the box for the category to Aggregate only non-empty grades. So I believe that an empty grade should be considered equivalent to a zero (at least that is the behavior I am expecting).

What I noticed was that the category average changed depending on which assignment was blank and which was zero. I would have expected the category value to remain the same. I am attaching the course backup (zip) to facilitate reproduction as well as two screenshots showing the swap between the 0 and blank on the last student with different calculated values for the assignment category.

Attachments

1. blankmin.png
132 kB
Anthony Borrow
2. droplowest_a.png
128 kB
Anthony Borrow
3. droplowest_b.png
129 kB
Anthony Borrow
4. droppingblanks.png
129 kB
Anthony Borrow
5. limits2.patch
2 kB
Petr Skoda

People

• Assignee:
Andrew Davis
Reporter:
Anthony Borrow
Peer reviewer:
David MonllaÃ³
Integrator:
Dan Poltawski
Tester:
Dan Poltawski
Participants:
Component watchers:
Adrian Greeve, Jake Dallimore, Mathew May, Mihail Geshoski, Peter Dias
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Watchers:
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Dates

• Created:
Updated:
Resolved:
Fix Release Date:
10/Sep/12