A trimmed mean is the mean of a dataset that has been calculated after removing a specific percentage of the smallest and largest values from the dataset.

For example, a 10% trimmed mean would represent the mean of a dataset after the 10% of values from the extremities of the dataset have been removed.

To calculate a trimmed mean in Excel you can use the TRIMMEAN function, which uses the following basic syntax:

TRIMMEAN(array, percent)

where:

• array: Range containing the dataset
• percent: Percent of data to exclude (between 0 and 1)

The following example shows how to use this function to calculate a trimmed mean in practice.

Example: Calculate Trimmed Mean in Excel

Suppose we have the following dataset in Excel:

We can use the following formula to calculate a 10% trimmed mean for this dataset:

TRIMMEAN(A2:A21, 0.1)

The following screenshot shows how to use this formula in practice:

The 10% trimmed mean of the dataset is 7.61.

In this particular dataset there are 20 total values. Thus, 10% of 20 is 2.

So, to calculate a 10% trimmed mean in this example Excel must remove two values from the extremities of the dataset.

We can confirm the formula is correct by manually calculating this trimmed mean ourselves:

10% Trimmed Mean: (2+3+3+4+5+6+7+7+7+7+8+8+9+10+11+12+14+14) / 18 = 7.61.

Note that in this particular example, the values that were removed from the extremities were clearly not outliers.

However, a trimmed mean is most useful in practice when there are extreme outliers in the dataset and you’d like to calculate the mean value without allowing these outliers to .

The following tutorials explain how to perform other common tasks in Excel: