# Aggregation Methods

• Moodle contains a number of aggregations that are used to calculate the totals for categories and for the course total in the Gradebook.  The three aggregation methods are documented below:

These are the three most common methods.  However the other aggregations can be accomplished using these three methods.  Each aggregation method is very different from the others, and can result in different grade totals.

## Sum of Grades

This aggregation method will sum up all of the points the student could receive.  This is the total number of points for the category.

### Example:

The Gradebook has 4 grade items, a 20 point quiz, a 10 point assignment, a 100 point mid-term exam, and a 200 point final exam.  The total possible points would be 330 points.

If the student receives 15 points on the quiz, 10 points on the assignment, 100 points on the mid-term, and 100 points on the final. Their total points would be 225 points.

 Sum of Points: 15 + 10 + 100 + 100 = 225 Category Total: 225 points

#### Important to remember:

• When the Sum of Grades aggregation method is used, Moodle sets the range as the sum of possible points for the category.
• An empty grade cell (no points have been entered) is counted by the aggregation as a zero.
• Because empty grades are treated as a zero the category total when displayed as a percentage or letter grade it will result in an inaccurate score until all points are entered into the gradebook.  In the example above, if the student has not taken the final exam the category total will display 115 points, but the range will still be 330 points and if displayed as a percentage the total would show 34.84% (115/330).

## Simple Weighted Mean of Grades

This aggregation method weights the grades based on the possible points for each grade item.  These grades are based on the value of the category total (default value is 100).  It is strongly recommended to leave the category total at 100 for this aggregation.  As an example a 20 point quiz would have a weight of 20, while a 200 point final would have a weight of 200.

### Example:

The Gradebook has 4 items, a 20 point quiz, a 10 point assignment, a 100 point mid-term exam, and a 200 point final exam.  The total possible points would be 330 points.

A student scores 15 on the quiz, 10 on the assignment, 100 on the mid-term, and 100 on the final.  Their score using Simple Weighted Mean of Grades is 68.18%.

 Raw Score: 15 out of 20 10 out of 10 100 out of 100 100 out of 200

 Sum of Weights: 20 + 10 + 100 + 200 = 330 Aggregation: (.75*20 + 1*10 + 1*100 + .5*200) / 330 = 68.1818 Category total: 68.18

#### Important to remember:

• This method will show the student's actual grade at any point in the semester.
• An empty grade cell (no points have been entered) is ignored by the aggregation until a numeric value is entered.
• The Simple Weighted Mean of Grades aggregation is equal to the Sum of Grades aggregation when the instructor sets the category total to 100.

## Weighted Mean of Grades

Weighted mean of grades permits the instructor to adjust the relative worth of a grade by applying weight factors. These factors are multiplied with the score to increase or decrease the final total for that grade item.  Grades are placed on a 100-point scale (normalized). For example if a student scores 9 out of 10 on a 10-point quiz, the score becomes a 90 after the normalization process.  Moodle multiplies the normalized score by the weight factor.  The weighted scores are then added together. The weights are also added together. Then Moodle takes the weighted scores and divides by the sum of weights to get the category total.

### Example:

The Gradebook has 4 items, a 20 point quiz weighed at 20%, a 10 point assignment weighed at 10%, a 100 point mid-term exam weighted at 35%, and a 200 point final exam weighted at 35%.  The total possible points would be 330 points.

A student scores 15 on the quiz, 10 on the assignment, 100 on the mid-term, and 100 on the final exam. Their score using Weighted Mean of Grades is 77.50%.

 Raw grade score: 15 out of 20 10 out of 10 100 out of 100 100 of 200 Normalized to 100-point scale: 75/100 100/100 100/100 50/100 Multiplied by weights: 75 * .2 = 15 100 * .1 = 10 100 * .35 = 35 50 * .35 = 17.5

 Weighted scores total: 15 + 10 + 35 + 17.5 = 77.50 Divided by sum of weights: 77.5 / (.2 + .1 + .35 + .35) = 77.50 Category total: 77.50%

#### Important to remember:

• The maximum points can be adjusted using this aggregation method. The default is 100.
• If the weights add up to 100 (or 1 if decimals are used), then they correspond to a percentage of the course or category total.
• The default value for a weight is 1 if no value has been set.
• If an item is assigned a weight of zero, the item counts as extra credit in the category.  Its earned points will still count toward the category total, but its possible points will not count toward the range total.
• If an item is assigned weight of 0.0001, that weight is too small to have an effect on the category total.

### Notes:

The name for the Moodle Gradebook (e.g. Gradebook Workshop) by default is the main category. Aggregation methods can be used in the Gradebook as a whole or on individual categories. You can apply different aggregations to different categories within the same Gradebook.

Settings for the aggregation methods are controlled in that categories configuration area. These settings effect the calculations of the items in that category. If a category has sub-categories then the aggregation method applies to the sub-categories total. Grade items in a sub-category are calculated based on the aggregation method for that sub-category. The sub-category can use a different aggregation than the parent category.