This blog post digs into the technical and mathematical aspects of how weight calculations in Blackboard work and the difference between weighting equally and weighting proportionately. There may come a time when a student in your class asks you to explain why their grade is what it is – and the information in this article could help you explain that to them.
Two Different Ways to Weight Categories
If you followed the steps from the previous article (PART 1), then you’ve likely got your grade center set up to weight by category. When weighting by category, there are two different options for how to distribute that weight to the assignment columns within that category: equally and proportionally.
- When using percentage for weighting equally, percentages are distributed equally among all assignments in a category regardless of their total point value.
- When using percentage for weighing proportionately, percentages are distributed based on the total points possible of the item (out of the total points possible for all assignments listed in that category)
If you use non-consistent total point values for your assignments (for example, if all of your tests are worth 200 points, your quizzes range from 10-100 points possible, etc), choosing to weight Equally or Proportionately will result in two completely different grades!
However, if you use consistent total points possible for all course items (for example, all course items have a total points possible of 100 points) or like items within a category – choosing to weight equally or proportionately will result in the same grade.
If you don’t weight by category and decide that you want to weight individual columns instead, Blackboard will not give you an option to weight equally or proportionately.
Example: Calculating Equal Category Weighting with Non-Consistent Total Point Values
Here is a simple example of how to calculate a weighted score where the categories are weighted equally with assignments that have non-consistent total point values within their category designations. We start out with a table listing the course assignments and the total points possible for those assignments.
Then we add in the student score (in points) that the student achieved on the assignment.
Now we calculate the student score as a percentage. When total points possible aren’t consistent, and weighting is done equally, Blackboard will convert student scores into percentages before applying category weighting. To calculate student score as a percentage, you take the student score and divide it by the total points possible for the assignment, then multiply by 100.
Fill in the right-most column of the table with the student score percentage:
In this example, we’re going to say that weighting for the categories is set up as follows:
- Tests – 60%
- Discussions – 25%
- Labs – 15%
When assignments are placed in one of these categories, the percentage of the category is equally distributed among all assigned columns. This allows for flexibility throughout the semester to add/remove assignments easily.
Once we have student score as a percentage, we can apply the column/category weighting to it. To calculate this, you would take the student score on the assignment (as a percentage) and multiply it by the weight that is assigned to that assignment column. See examples below.
The table below shows the breakdown of weights for each assignment (by category), what the student score was as a percentage and then the student score with the column weight applied to it. In this example, the “Test” category is 60% of the student’s overall grade. Because we know this and we know that the weighting is set to “equal” for this category, we can see that each assignment column that belongs to that category (there are three tests) get an equal part of that 60% (for three columns, each one gets 20% of the overall grade). The same observation can be made when viewing the “Discussion” category (total category weight is 25%, and there are 4 columns in the category, so each column equally gets 6.25% of the overall weight) and the “Labs” category (total category weight is 15%, and there are 3 columns in the category, so each column equally gets 5% of the overall weight).
Once weights are applied to the student score, the column for weighted student score can be summed to get the total weighted score for the student.
If all the above information were set up in a Blackboard grade center, the score that appears in Blackboard would match what was manually calculated above:
Example: Calculating Proportionate Category Weighting with Non-Consistent Total Point Values
It is easier to look at a per-category basis when doing proportionate weighting. Proportionate weighting will only affect categories where assignments within the category don’t share the same total points possible values. We’re going to use the same example above and change the category weighting to be proportionate instead.
To get the category total weighted score, you will use the following formula on each category:
Student Score Total for Category / Total Points Possible for Category * Category Weight * 100 = Category Score (in percent)
Category: Tests is worth 60%
583 / 700 * .60 * 100 = 49.971429%
Category: Discussions is worth 25%
26 / 40 * .25 * 100 = 16.25%
Category: Labs is worth 15%
90 / 110 * .15 * 100 = 12.272727%
Final Total Weighted Score
Add all category scores together: Tests + Discussions + Labs = Final Score %
49.971429 + 16.25 + 12.272727 = 78.494156
If we adjust our settings in Blackboard to match the example above, we’ll see that it comes up with the exact same score that we just calculated manually.
Wrapping Up
As you can see by the calculated examples above, both use the same categories and the same student scores. But, calculating based on equal weighting across a category and calculating based on proportionate weighting across a category CAN produce different grade results (especially when non-consistent total point values are used for assignments within the same category). Make sure to keep this in mind when you are trying to determine how you would like to weight grades for YOUR class!