Productive impact is Impact less any Rework (cases where an individual rewrites code they recently wrote), and is a blend of both activity level and efficiency.

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. 

In the analytics module, this will be the sum of the productive impact scores of all commits made over the selected time period.

While Impact represents activity and the difficulty and magnitude of that activity, Productive Impact better represents the eventual outcome of that activity. 

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.
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