General help

 
 
Picture of Doug Moody
Please Help Me With Some Math
Group Particularly helpful Moodlers

I am not that great with math, so could someone help me understand math weightings?

Here is the scenario...I teach a class with 4 categories (Lessons, Projects, Participation and Exams) Each category has a different weight. Lessons = 40%, Projects = 30%, Exams = 20%, Participation = 10%.

My question is that when I set up my Categories and Items gradebook, and assign a weight, what should I type in the box for each assignment (given the above parameters)? Should it be 40, 30, 20, 10 respectively, or, because I grade on points, should it be .4, .3, .2, .1. Or, maybe some other numbers. I am just not sure.

Thanks.

 
Average of ratings: -
Picture of Doug Moody
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

I just did some more figuring, and ran into a different dilemma. In addition to my earlier posting, there's another problem. PLEASE help..

Anyway, let's say I had 8 assessments worth 48 total points. Some are 2 pointers, some are 10 pointers.

Using weights, I would think the fairest way to do this would be to take the total points possible and divide by the total points earned. (48/8) However, at times, some students do not turn in an assignment. In those cases, if it were a 10 point assignment, they might earn a zero.

With weights, the zero vastly outweighs several other assessments that might add up to 10, so just missing one 10 point assignment, if I give a zero, would blow out his weightings and skew his grade.

So, it would seem fairer for me to divide the number of actually handed in assessments by the number of possible points handed in. In this example, 38 possible points instead of 48. Then, when he DOES hand in the 10 pointer, I could again add in the additional 10 possible points.

This seems more fair because I want students to see what they are doing at any moment in time, not what their grade MIGHT be.

Has anyone solved this dilemma? For me, it is about educational philosophy as much as it is about math, so that's why I am asking it here in the general help section.

Thanks again.

 
Average of ratings: -
Floyd Saner - Tail of the Dragon, U.S. 129, NC
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

Doug,

Re: your 2nd question.  If I understand you correctly, what you want should happen by default if you are using a recent version of Moodle.  The default setting is 'Aggregate only non-empty grades'.  Moodle correctly adjusts the divisor (the sum of the weights) according to the graded items that have a grade.  If a grade is left blank, it is totally ignored.  Only when you enter a number, including a zero, does the item get included in the total aggregation.

If your system counts empty grades as zero, then you need to change a setting:

In the course grade book, go to 'Categories and Items',  click the Edit icon to edit the category settings, the select 'Aggregate only non-empty items'.  You may need click the "Show advanced" button.

To make a system-wide change for all courses:  Go to 'Site administration...Grades...Grade category settings'. 

-Floyd

 
Average of ratings: -
My Picture
Re: Please Help Me With Some Math
 

Hi Doug,

I have been using weights for years and have always use the whole numbers. Although, I believe either would work.

Caryl Gordon

 
Average of ratings: -
Floyd Saner - Tail of the Dragon, U.S. 129, NC
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

Doug, it does not matter whether you use whole numbers or decimals as long as you are consistent.

Weighting by 40, 30, 20, 10  will calculate a final result exactly the same as weighting by 0.4, 0.3, 0.2, 0.1.

If Wx is a weight and Gx is a grade, then the aggregation is

(W1*G1 + W2*G2 + W3*G3 + W4*G4) / (W1 + W2 + W3 + W4) 

 
Average of ratings:Useful (1)
Picture of Doug Moody
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

First THANK YOU EVERYONE for trying to help me. I have done as you all instructed, but from what I can see, Moodle is messing with the math and it isn't working correctly, even though I have done all that you told me to do. I have included some graphics to illustrate.

First, here is how my categories are set up. I use points, not percentages, which is why I decided to not use weights, just mean of grades. There are also two assessments that are separate and connected, so they aren't part of the calculations. I typed in the 48 at the bottom because that is the total possible number of points that can be earned in this category.

 

 

Next is the image of a typical grade a student sees. You can see that the total points aren't being added correctly, as it is showing 40.5 points earned, and it is dividing that number into 48, arriving at the 84.5%. This is an incorrect calculation. It OUGHT to be 27.8 points total. I have double checked his grades, and they are correct.

 

So where is this bogus number coming from? Ideas?

 

 

 
Average of ratings: -
Picture of Bob Puffer
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

IMO you should only enable SWM and WM as aggregation types. All of the other aggregations use 'funny' math to achieve their result.

When we talk about weights, all grades are weighted.  SWM uses the maximum earnable grade as the relative weight.  If that doesn't meet the need, WM adjusts that number to reflect the desired weighting.  I believe this was well understood by Nicolas when he wrote the original 1.95 gradebook.

 
Average of ratings: -
Picture of Doug Moody
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

Bob,

So then, why am I seeing the wrong totals on the points? If using points, then weighting is automatically built in, so SWM or WM isn't relevant. I am using "real" as the grade. In the example I provided, it is totaling wrong on the total points, although I manually inputted 48 as the total possible points, it isn't dividing by correct amount of points. It has some odd number that I don't know where it is coming from (40.6) It should correctly be using 27.8 (the total points actually earned)

Also, if aggregation was working right, then the total possible points ought to adjust automatically to the amount of points available to calculate against, not 48. In this case, the calculation should have been 27.8/34.

Is this a moodle bug?

 
Average of ratings: -
Floyd Saner - Tail of the Dragon, U.S. 129, NC
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

Doug,

So, here is what is happening.  You have the category aggregation set as Mean of Grades.  With that aggregation method the percent grade values are averaged - all weighted equally, regardless of the number of points.  Mean of Grades ignores points.

In your case Moodle calculates the overall percent in the following manner:

(100% + 77.9% + 8% + 80%)/4 = 84.5%  (rounded up from 84.48%)

You set the total number of points to 48, so Moodle then calculates the 'equivalent' number of points to correspond to 84.5%,  i.e. 48 * 84.5% = 45 points.  I believe it is this 'equivalent' point calculation that Bob refers to as 'funny math'.

If you want the grades to be weighted by the number of points, then use Simple Weighted Mean of Grades.  That should result in an overall grade of 81.8 (rounded from 81.76) in your example.  

-Floyd

 
Average of ratings: -
Picture of Doug Moody
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

Floyd,

Thank you SO much. You helped me solve the largest part of the puzzle because the correct percentage is working. I deleted the manual entering of points and changed to simple weights. But there is still one anomaly that is puzzling me. I included a graphic below. For some reason, the total earned points is not showing up. I circled and annotated it in the graphic.

Can you maybe tell me why it isn't working ? Thank you again.

 
Average of ratings: -
Floyd Saner - Tail of the Dragon, U.S. 129, NC
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

Doug,

As I understand the grade book, "Mean of Grades", "Weighted Mean of Grades" and "Simple Weighted Mean of Grades" all work with percentages - the grades are first converted to percentages, then aggregated according to the the method specified.  That aggregated percentage is then displayed in the percentage column.   Moodle then takes the Maximum Grade number, specified in the Category setup page, and calculates what an equivalent number number of points would be.  So, in your example, the Simple Weighted aggregation is 83.5%.  The Maximum Grade number for the category is 100.  So the 'equivalent' number of points earned must be 83.5 points.  If you change the Maximum Grade for the category to 34 (4 + 10 + 10 + 10), the sum of the max grades of the marked items, then the total number of points would calculate to 34 * 83.5% = 28.4.

If you want points to be used for the calculations, you will need aggregation method "Sum of grades".  Have you looked at http://docs.moodle.org/24/en/Category_aggregation

 
Average of ratings: -
Picture of Bob Puffer
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

This is why I wrote the LAE Grader report -- Moodle insists that nobody would ever use 'points' for grading and their 'real' grade is just a restatement of percentage.

 
Average of ratings: -
Picture of Doug Moody
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

Floyd and BOb (and all others who helped me)

First, let me say THANK YOU. I managed to slog through this with your guidances. I think the key was Floyd showing me that I had to use Sum of Grades. I guess I didn't make that clear from the start, so I kept trying to make it work with Simple Weighted.

BTW, Bob, I use  your fine LAE Grader report plugin. It helps a lot. Thank you for that.

Yet, there is still a minor problem. It might not be solvable, but if you know the reason it is happening, please let me know. Then it would be perfect. smile

The graphic below illustrates. But in short, I assumed that if I use aggregation, then any grades not earned wouldn't be included in the range. Yet it is! Why is that? I circled the problems below. The assignment called Blocks hasn't earned any points, yet the addition of the range (0-28) still includes the range for Blocks and adds up the entire category's possible points. It shouldn't include it until there is a value for that assessment.

This problem also shows up at the bottom for Total Possible Score. 416 points are not possible in this report, but what Moodle is doing is counting all the hidden assignments in a category that doesn't shown in this report. Those assignments will be, in the future, included, but not at this point. Naturally a 56.99 divided into 416 points will equal an F. But in reality, the student ought to get a total score which is an aggregation of only those assessments he has completed. Each category is reporting correctly UNLESS a student misses an assessment, as in the Lessons category. So, this student doesn't really have a 66.4%, he has 18.6/26 = 71.5

 So, is it possible to fix this?

 
Average of ratings:Useful (1)
Picture of Bob Puffer
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

Sum of grades does not exclude non-graded items from the aggregation.  I've turned it off on our site. SWM would be the suggested alternative though it doesn't maintain accurate category and course total points.  I've hacked our User report and the Categories and items screen in order to make it do that.

 
Average of ratings: -
Picture of Doug Moody
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

Bob,

Can you share with us how you did the hack? Would it give me the column displayed as I need?

 
Average of ratings: -
Picture of Bob Puffer
Re: Please Help Me With Some Math
Group Particularly helpful Moodlers

I'm glad to share the hacks but I probably should package them as an LAE User report like they were in 1.9 (thought I could get away without doing that).  However my hacks don't correct the problem of Sum of grades not excluding ungraded items.  You need to go to SWM which, with my hacks would display the column the way you want it.

I'll work on LAE User report.

 
Average of ratings: -