How are Standard Deviations Calculated

This standard formula is used to calculate the standard deviation:

standard deviation = sqrt [(B - A^2/N)/N]

where: A B N

The standard deviation calculations differ based on the type of metric used:

  • If the time rollup type = Sum or Average
  • If the cluster rollup type = Individual or CollectiveThe cluster rollup type is applicable only at the tier or app level (node-level metrics will have the same calculations).

This example shows a standard deviation using metric types of:

  • Time rollup type = Average
  • Cluster rollup type = Collective
Metric - Calls Per Minute (Average, Collective)
(Hourly Metric Table)
Time Sum Count Weight-Value Weight-Value-Squared 
                09:00
180 2 180 300 
                10:00
300 2 300 780 
                11:00
150 2 150 195

For these metric values, the baseline of type = All Data

With daily, weekly, or monthly seasonality, the data points considered are values for the same hour for all days, the same day of the week, or the same day of the year, respectively.

In this case, the baseline calculations will be:

Value (180+300+150)/360 = 1.75

Standard deviation sqrt(((300+780+195) - (((180+300+150)^2)/360))/360) = 0.69