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diff --git a/web/api/queries/stddev/README.md b/web/api/queries/stddev/README.md new file mode 100644 index 0000000..7cd7d62 --- /dev/null +++ b/web/api/queries/stddev/README.md @@ -0,0 +1,93 @@ +<!-- +title: "standard deviation (`stddev`)" +custom_edit_url: https://github.com/netdata/netdata/edit/master/web/api/queries/stddev/README.md +--> + +# standard deviation (`stddev`) + +The standard deviation is a measure that is used to quantify the amount of variation or dispersion +of a set of data values. + +A low standard deviation indicates that the data points tend to be close to the mean (also called the +expected value) of the set, while a high standard deviation indicates that the data points are spread +out over a wider range of values. + +## how to use + +Use it in alarms like this: + +``` + alarm: my_alarm + on: my_chart +lookup: stddev -1m unaligned of my_dimension + warn: $this > 1000 +``` + +`stdev` does not change the units. For example, if the chart units is `requests/sec`, the standard +deviation will be again expressed in the same units. + +It can also be used in APIs and badges as `&group=stddev` in the URL. + +## Examples + +Examining last 1 minute `successful` web server responses: + +-  +-  +-  +-  + +## References + +Check <https://en.wikipedia.org/wiki/Standard_deviation>. + +--- + +# Coefficient of variation (`cv`) + +> This query is also available as `rsd`. + +The coefficient of variation (`cv`), also known as relative standard deviation (`rsd`), +is a standardized measure of dispersion of a probability distribution or frequency distribution. + +It is defined as the ratio of the **standard deviation** to the **mean**. + +In simple terms, it gives the percentage of change. So, if the average value of a metric is 1000 +and its standard deviation is 100 (meaning that it variates from 900 to 1100), then `cv` is 10%. + +This is an easy way to check the % variation, without using absolute values. + +For example, you may trigger an alarm if your web server requests/sec `cv` is above 20 (`%`) +over the last minute. So if your web server was serving 1000 reqs/sec over the last minute, +it will trigger the alarm if had spikes below 800/sec or above 1200/sec. + +## how to use + +Use it in alarms like this: + +``` + alarm: my_alarm + on: my_chart +lookup: cv -1m unaligned of my_dimension + units: % + warn: $this > 20 +``` + +The units reported by `cv` is always `%`. + +It can also be used in APIs and badges as `&group=cv` in the URL. + +## Examples + +Examining last 1 minute `successful` web server responses: + +-  +-  +-  +-  + +## References + +Check <https://en.wikipedia.org/wiki/Coefficient_of_variation>. + +[](<>) |