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<!--
title: "Trimmed Mean"
description: "Use trimmed-mean in API queries and health entities to find the average value from a sample, eliminating any unwanted spikes in the returned metrics."
custom_edit_url: https://github.com/netdata/netdata/edit/master/web/api/queries/trimmed_mean/README.md
-->
# Trimmed Mean
The trimmed mean is the average value of a series excluding the smallest and biggest points.
Netdata applies linear interpolation on the last point, if the percentage requested to be excluded does not give a
round number of points.
The following percentile aliases are defined:
- `trimmed-mean1`
- `trimmed-mean2`
- `trimmed-mean3`
- `trimmed-mean5`
- `trimmed-mean10`
- `trimmed-mean15`
- `trimmed-mean20`
- `trimmed-mean25`
The default `trimmed-mean` is an alias for `trimmed-mean5`.
Any percentage may be requested using the `group_options` query parameter.
## how to use
Use it in alarms like this:
```
alarm: my_alarm
on: my_chart
lookup: trimmed-mean5 -1m unaligned of my_dimension
warn: $this > 1000
```
`trimmed-mean` does not change the units. For example, if the chart units is `requests/sec`, the result
will be again expressed in the same units.
It can also be used in APIs and badges as `&group=trimmed-mean` in the URL and the additional parameter `group_options`
may be used to request any percentage (e.g. `&group=trimmed-mean&group_options=29`).
## Examples
Examining last 1 minute `successful` web server responses:
- 
- 
- 
- 
## References
- <https://en.wikipedia.org/wiki/Truncated_mean>.
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