This article contains answers to questions Sisu users commonly ask. New Q&As are added as they come, so bookmark this article and check back often.

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**What are the changes in how Impact is calculated for Average/Rate metrics for Comparison Analyses? Why did Sisu make these changes?**

On May 19, 2021, Sisu introduced a new method for calculating Impact**.**

The reason Sisu developed this new model is twofold:

- It
**better matches the business logic**that most business analysts use to calculate how much a certain population caused an overall metric to change, expressed as Impact. - It is
**mathematically better**than the original model.

The original method determined impact looked at *how much of the delta (change) between periods/groups would be changed due to the presence of the subgroup***.**

The new method of determining impact looks at *how much the subgroup contributes to the change*. It does this by calculating the sum of Impact of mutually exclusive, collectively exhaustive (MECE) Subgroups which adds up to the overall change in the Metric. Subgroups that have no change in their metric value or row count show up as zero impact.

The formula used in the new method is:

This new method results in greater accuracy in the Impact ratings for your Subgroups than before, allowing for even greater confidence in your Analyses.