Please note the final paragraph on this page which is from Moodle.org. Rubric grade calculations often yield unexpected results.
Valid for Moodle 2.8. Checked on 0/21/2015.Rubric grades are based on the minimum and maximum grades possible for each criteria. The calculations involves summing up the difference between the minumum grade possbile and the grade given for each criteria and then dividing the result by the sum of maximum number of points possible minus the sum of minimum points possible. The resulting percentage is then applied to the number of points for the overall assignment.
In the words of moodle.org's page on rubrics:
The rubric normalized score (ie basically a percentage grade) is calculated as
- where is the number of points given to the i-th criterion, is the minimal possible number of points for of the i-th criterion, is the maximal possible number of points for the i-th criterion and is the number of criteria in the rubric.
Example of a single criterion can be: Overall quality of the paper with the levels 5 - An excellent paper, 3 - A mediocre paper, 0 - A weak paper (the number represent the number of points).
Example: let us have an assessment form with two criteria, which both have four levels 1, 2, 3, 4. The teacher chooses level with 2 points for the first criterion and 3 points for the second criterion. Then the normalized score is:
Note that this calculation may be different from how you intuitively use rubric. For example, when the teacher in the previous example chose both levels with 1 point, the plain sum would be 2 points. But that is actually the lowest possible score so it maps to the grade 0 in Moodle. To avoid confusion, it is recommended to always include a level with 0 points in the rubric definition.