The aggregation function is part of the definition of the KPI's performance target. The aggregation function tells the system how to merge (or Aggregate) multiple measurements over a number of periods in order to determine whether a party has passed or failed.

The are a number of ways in which multiple values can be aggregated, each producing a different result. You need to decide which type of aggregation is required to make your KPI target meaningful. The options for the aggregation functions are shown below.

*Fig 1 - Options for the Aggregation function*

**Calculation Differences for Aggregation Functions**

In order to demonstrate the difference between each of the aggregation function options, the following measurements are based on a ratio KPI:

**Measurement 1: 4/8Measurement 2: 2/10Measurement 3: 1/4**

The table below shows the calculation that is performed in order to determine the aggregated value.

**Tip: When dealing with Ratio Type KPI's, the most common and widely accepted aggregation function is Ratio Total**

Function | Calculation | Result |

Average | ( (4/8)+(2/10)+(1/4) ) / 3 | 0.316 or 31.6% |

Count | there are 3 measurements | 3 |

Total | (4/8) + (2/10) + (1/4) | 0.95 or 95% |

Ratio Average | ( (4 + 2 + 1) / 3) / ( (8 + 10 + 4) /3 ) Average of the numerators divided by the average of the denominators | 0.318 or 31.8% |

Ratio Total | (4 + 2 + 1) / (8 + 10 +4 ) Total of the numerators, divided by the total of the denominators | 0.318 or 31.8% |