Grade Calculations

GB2 Grade Calculations

The calculations for the new gradebook have two main modes:

• points-based calculations : in which the ratio of an item's max points versus the total points possible for all items scored is used to establish the item's 'weight' within the gradebook
• weight-based calculations : in which the product of two assigned weights at the category and item levels is used to establish the item's 'weight' within the gradebook

Points Based Calculations

There are two cases for points based calculations, but the distinctions between the two are very slight. Whenever the 'organization' of the gradebook is set to "No Categories" or "Categories", points-based calculations will be used, independent of whether the "grade type" is set to "poe ints" or "percentages". In setting up the gradebook, an instructor must provide a maximum number of points per item, or if one is not entered, a default value of 100 will be used.

So, in "No Categories" mode, we might create the following gradebook:

• My Default Gradebook
  • Item 1 (25 points)
  • Item 2 (25 points)
  • Item 3 (25 points)
  • Item 4 (25 points)
  • Extra Credit Item (10 points)

This gradebook would have a total possible non-extra-credit point value of 100, with 10 extra credit points possible.

Each student's course grade is then calculated according to the point value (or in percentages mode, the percent of max points) assigned by the instructor, as per the following equation:

S = sum of all non-extra-credit points earned
E = sum of all extra-credit points earned
P = sum of all non-extra-credit points possible

% score = (S+E)/P

Of course when we include the ability of instructors to excuse an individual student from an individual item, we discover that P can vary on a student-by-student basis, as shown below:

Note that in this case "Joe" gets more of a boost from his 10 point extra credit item than Melody does, simply by virtue of having been excused from one item . . . this is logical, since 10/75 (0.133) is larger than 10/100 (0.100), but it may be unintuitive at first glance to some instructors.

In "Categories" mode, calculations are still point-based, and work along the same fundamental principle, though when it comes to extra credit there is a further complication. By organizing the points into categories, we end up with the idea of an item that contributes extra credit to that category specifically, where it doesn't make sense to determine the category contribution to the overall score unless at least one non-extra-credit item has been graded for that category.

• My Default Gradebook
  • Category 1
    • Item 1 (25 points)
    • Item 2 (25 points)
    • Item 3 (25 points)
    • Item 4 (25 points)
    • Extra Credit Item (10 points)

So under this case, we have the same basic calculation as above, but if we add a student who only completed the extra credit item, we get another non-intuitive case:

As you can see, it is not possible to calculate a 'category score', or in the case of this gradebook, a course grade, for Francis... s/he has received 10 extra points, but since P is zero, we get a division by zero exception.