# Category aggregation

This menu lets you choose the aggregation strategy that will be used to calculate each participant's overall grade for this category. The different options are explained below.

Important: An empty grade is simply a missing gradebook entry, and could mean different things. For example, it could be a participant who hasn't yet submitted an assignment, an assignment submission not yet graded by the teacher, or a grade that has been manually deleted by the gradebook administrator. Caution in interpreting these "empty grades" is thus advised.

Strategy | Description
--- | ---
Mean of all grades | All grades are added up, then divided by the total number of grades. Empty grades are included (they are interpreted as the item's minimum value).
Mean of non-empty grades | Same as above, except that empty grades are ignored.
Median of all grades | The median is calculated by counting all the grades and selecting the grade that falls in the middle of that count (or the mean between the two middle grades if there is an even number of grades). The advantage over the mean is that it is not affected by outliers (grades which are uncommonly far from the mean). Empty grades are included.
Median of non-empty grades | Same as above, except that empty grades are ignored.
Smallest grade of non-empty grades | Only the smallest grade is kept. Empty grades are ignored.
Highest grade of non-empty grades | Only the highest grade is kept. Empty grades are ignored.
Mode of all grades | The mode is the grade that occurs the most frequently. It is more often used for non-numerical The advantage over the mean is that it is not affected by outliers (grades which are uncommonly far from the mean). Empty grades are included.
Mode of non-empty grades | Same as above, except that empty grades are ignored.
Weighted mean of all grades | Each grade item can be given a weight, which is then used in the arithmetic mean aggregation to influence the importance of each item in the overall mean. Empty grades are included.
Weighted mean of non-empty grades | Same as above, except that empty grades are ignored.
Mean of all grades (extra credits) | Arithmetic mean with a twist. An old, now unsupported aggregation strategy provided here only for backward compatibility with old activities. Empty grades are included.
Mean of non-empty grades (extra credits) | Same as above, except that empty grades are ignored.