Impact reports either:
How much a pattern pushes the overall data selection measure up or down, or
How much a sub-pattern pushes a pattern measure up or down
For example, if the Overall NPS for your selected data is 59 and a pattern has an impact of -12.5, this means the pattern is contributing -12.5 points to the Overall NPS of 59, and without the negative contribution from this pattern the Overall NPS would be 12.5 points higher (71.5).
Impact Calculation