# Approximate median calculation

Use the approximate median to calculate the center value of a data group
in which strong outliers might distort the outcome.
In Pega Platform, you determine median by using the low-storage and low-latency
approximate calculation method.

## Behavior

Consider the following points when selecting the approximate median as your
aggregation calculation method:

- Event strategy windows calculate median on the fly, constantly converging toward or oscillating around the actual median value.
- If the event strategy window consistently aggregates values above or below the current median, the median value increases or decreases accordingly. The speed with which the median moves up or down the value range depends on the distribution of values that the window aggregates.
- The size or type of the window does not affect the calculation outcome.
- The approximate median is always calculated from the start of the data flow that references the event strategy.
- The calculated median value is meaningful only when you aggregate unsorted or randomized values.

## Replacement for exact median calculation

The approximate calculation method replaces the exact median calculation because it requires fewer system resources for storing or sorting incoming values. The median calculation method for event strategies that you created prior to Pega Platform 8.4 does not change until you edit and save the aggregation calculation options. The approximate calculation is the only method available for median in release 8.4 and later.