Calculation: Impact is a synthetic measure we developed to help teams understand the significance of all the changes to the code. Rework is the percent of code that was written within the last three weeks that has been edited by the same reviewer.
Productive Impact thus measures the magnitude of the changes to the codebase, adjusted to exclude anything work that was later revised. For example:
If an engineer has an Impact of 1000, but a 10% rework rate, her productive impact would be 900.
Why it matters: While Impact represents activity and the difficulty and magnitude of that activity, Productive Impact better represents the eventual outcome of that activity.
How to use it: If Impact is high and rework is high that can indicate that a developer is working rapidly, but may be stuck due to unclear requirements, misalignment on technical direction, on lack of familiarity with the codebase.