[ARCHIVED] Has anyone seen Canvas incorrectly calculating an Assignment Category?

[oneill_edward]

A professor I support showed me this.

Three grades in an Assignment Category.

Two are out of 20, one is out of 25.

When Canvas calculates the grade for the Category, it gives the result as if all three grades had the same weight.

Does Canvas not know how to do a weighted average? It can't be adding the scores and dividing by 65 to get the percentage--because it's getting the wrong answer.

Thoughts?

[JamesBodurtha]

I was looking for information regarding the precision of assignment grade weights.  My experience says Canvas doesn't allow alternative weights in an assignment group.  In your case, just to get it to work and say the assignments are homework, I'd allocate 40% to a 20point HW group w/two assignments and 25% to a 25p HW group w/one assignment.  Junks up the assignment page, but I haven't stumbled on any options to do it differently.    My sort of analogous problem is having 3 quizzes in a group and have a group weight not divisible by three.  Students ask what the actual weights are and benchmarking against a spreadsheet record is off a bit.   What is the format of assignment weights in grade calculations

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[oneill_edward]

So Canvas assumes each Assignment in an Assignment Group are weighted equally? Since in my case, the instructor was using points, it would be trivial to add the points and THEN divide by the total possible points. Instead, Canvas seems to treat each grade as a percentage and then to average them (non-weighted). Is that your experience, @JamesBodurtha?

[Ron_Bowman]

@oneill_edward 

I use a weighted gradebook, and for my assignment groups it takes total points earned divided by total points possible to get a percentage that is then multiplied by the group weight.  It is not taking percentages of the assignments and averaging them.  I do not have a drop lowest or drop highest selected.  You did not mention that directly, but from the information posted I would assume it is not (just threw that out there in case that has an affect on the way canvas treats grades).

Can you supply the actual numbers for what you are discussing?

[lohs3602]

I remember a couple of years ago, Canvas changed how it calculated these, and I was trying to remember what it did currently. So here I am. Judging from your comments and my vague memories, Canvas USED TO weight all assignments within a category equally. So if you had 4 exams that together were worth 40% of the course grade, each was worth 10%, regardless if one had 65 pts, another 80, etc. A few years ago, this changed so that it adds all the points earned within the category and divides by the points possible, so that exam with 80 pts would effectively carry more weight than the 65-pt one. The solution, as suggested above, is to make Exam 1 its own group worth 10% and so on. On Blackboard you could choose which method you preferred for each assignment group. Doesn't seem like that should be so hard of a feature to include...

[Ron_Bowman]

@lohs3602 You are correct - probably not hard to do - unless Blackboard has a patent on that feature.

[Tanya_Blacic]

Here is what seems to be an even simpler example of incorrect calculations in an assignment group:

I have an assignment group with nine assignments in it, all of which are worth 5 points and a drop lowest rule. For a student who missed one assignment and got a zero on it (correctly chosen as the one to drop by Canvas) the remaining scores are 4/5 on two assignments and 5/5 on the other six assignments. So this student has a total of 38 points in this assignment group. I would calculate the score in this group as a percentage as 38/40*100% = 95%. Canvas somehow reports the student's score in this group as 96.67%.

How on Earth does Canvas come up with this? It can't be a weighting issue since every assignment in this group is worth the same number of points. I am using a weighted gradebook and this particular assignment group is worth 20% of the total score in the class, but I don't see how that would affect the total for the group itself.

What I can say is that this only seems to be a problem with assignment groups that have a drop lowest rule. Compared to my manual calculations in Excel, scores for groups with a drop lowest rule will differ by several percentage points with the Canvas calculations being either higher or lower than my Excel calculations.

If I can't tell how Canvas is coming up with these numbers, there's no way I can use this to actually determine students' scores. Guess I'm back to doing it all in Excel where I can at least see how the calculations are being done, and I'll have to just warn my students that the numbers they see in Canvas are probably WRONG.

[Chris_Hofer]

Hello @Tanya_Blacic ...

Full disclosure...  I am a former Canvas administrator in higher education, and I did not teach courses in Canvas.  That being said, although I am not 100% certain of this, I *think* your example you have described with the scores you have provided is similar to the example given in the light blue box of this Guide:

How do I create rules for an assignment group?

The paragraph I'd point out to you is this (highlighting is my own):

Dropping scores is based on the impact to the total points for that assignment group. In some cases, the point value may be considered more important than percentage score when determining which assignment to drop. For example, if a student earns 100% on a 50-point assignment, 65% on a 100-point assignment, and 50% on a 24-point assignment, the student’s total score is 127 out of 174 points, or 73% for the assignment group. If an instructor sets a rule to drop the assignment with the lowest score in the assignment group, Canvas will drop the score that gives the student a better total score for the group. Even though the 50% score is the lowest percentage, the assignment with the 65% score will be dropped, giving the student a score of 62 out of 74 points, or an 84%, for the assignment group.

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Do you think this is what is happening with the calculated percentage for your assignment group?

Looking forward to hearing back from you on this!

[Tanya_Blacic]

I did see that example, but I don't think that's what happening in my course because all the assignments in my group are worth the same amount of points. Canvas does seem to be correctly choosing the right score to drop (in my example, the one the student got a zero on is definitely the one to drop), but then when it calculates the total score for that assignment group it gives an incorrect result. For other students in this course, the Canvas-calculated total for the assignment group is sometimes higher than what I calculate it should be and sometimes lower - doesn't seem to be a consistent error.

I do have two other courses this term that use assignment groups with the drop lowest rule applied and I only see this incorrect calculation in one of my three courses. The IT folks at my college have started a support ticket with Instructure to look at this, but it does suggest that it might be wise to check what Canvas is doing if you are using the drop lowest rule. I guess I can't avoid doing grade calculations in Excel after all if I feel like I can't trust what Canvas is doing and have to check it every time just in case. 😑

If we get the issue resolved via Instructure support I'll try to remember to come back here and update.

[Tanya_Blacic]

We figured out the problem. A single assignment worth a different amount of points had been incorrectly placed in the group and this threw off the calculations. Probably it was just my mistake not noticing that an assignment had been classified wrong.

A warning to check your assignment groups to make sure everything is where it should be... 😅

[Chris_Hofer]

Hi @Tanya_Blacic ...

Thank you for coming back to provide an update.  I am glad that you were able to get this figured out on your end!