Definition of a Stability Metric

This is the short “just the facts” version of a longer post I’m writing on the motivations and potential benefits of tracking Stability. Here, I’m just describing the formula.

“Stabilty” is a measure of the portion of planned work that is executed, relative to the total work considered in an iteration, including additions and subtractions. It correlates to churn and waste and provides focus for introspection and improvement.

Stability was developed for teams using Scrum. It is based on estimation of effort for items being worked on in a time-boxed iteration. Any unit of effort can be used (story points, ideal days, etc.)

P = Planned work: the work the that the team committed to for the iteration.

A = Added work: the work that is added to the iteration in progress.

R = Removed work: the unstarted work that is removed from the iteration in progress.

WS = Stable work: the amount of work that was planned and ultimately worked on in the iteration.

WS = P – R

WU = Unstable work: the part of the work the was added or removed.

WU = A + R

S = Stability, the ratio of stable work to all work that was considered, from plan to execution.

S = WS / (WS + WU)

This reduces to:

S = (P – R) / (P + A)

Coming: more detailed thoughts on the value and application of Stability and Doneness metrics in iterative teams.

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