Scrum Point Accounting for Unfinished Stories

Here’s one for the Scrum nerds out there.  Working with Joe Justice of Wikispeed, I cooked this post up because this is the last time I want to have to refigure this out from scratch.

beancounterThere’s a point that comes up every time I train or coach Scrum teams related to whether or not you re-estimate a story that was unfinished at the end of last sprint when you take it into the next sprint.  It drives me crazy because I personally despise hour-based project management accounting and these sorts of questions evoke bad memories of waterfall projects and PMP project managers.  I’m also really bad at math.

So let’s take a look at what happens when a story is half-finished and carried over to the next sprint by teams using different accounting methods.

conservationofpoints

The chart above shows the burndown for a hypothetical 40 point release (eight  5 point stories) by three different 10 point teams.  All three teams completed the release.  Team 1, in blue, burned down the project smoothly 10 points per sprint.  Don’t laugh, it could happen!  No accounting issue there.

Team 2 didn’t complete one of the 5 point stories in sprint 1 and got 0 points for it in that sprint.  They took it into Sprint 2 as a 5 point story, completed it along with two more 5 point stories.  They recorded 15 points of velocity for Sprint 2 and got back on the ideal burndown for the rest of the release, burning those 40 points down to 0.

Team 3 also didn’t complete one of the 5 point stories in sprint 1.  They also took that story into Sprint 2, but re-estimated it at 2 points.  They completed that incomplete story, now valued at 2 points along with two 5 point stories the same as Team 2.  But because they re-estimated the remaining work on the unfinished 5 pointer as 2 points, they recorded only 12 points of velocity where Team 2 recorded 15 for the exact same amount of work.  Essentially, the release lost 3 points of work.

Shrinkage

The method team 3 used, and the one I’ve advocated up until recently, I call Shrinkage.  That’s because the amount of points recorded to complete the release goes from 40 to 37 when the unfinished 5 point story gets re-estimated.  3 points simply disappear from the release.  I like it for some very tactical, team psychology, Scrum Master oriented reasons:

  • It forces us to be honest about the work
  • It helps teams avoid the trap of simply taking the product backlog estimate of a story into the sprint backlog
  • It reinforces the notion that incomplete work is waste
  • It exercises the team’s relative sizing muscle

Conservation of Points

The method of team 2, where they didn’t re-estimate the remaining work but simply took the story into the next sprint at the original estimate I call Conservation of Points.  The three points of work on the unfinished story in Sprint 1 are carried over into Sprint 2 and accounted as Sprint 2 velocity even though the work was done in Sprint 1.  No points disappear from the release.

Recommendation

I recommend using Conservation of Points now for one, and only one reason.  In a Shrinkage model, in order for the release burndown to continue to fulfill its purpose, the product owner needs to account for the lost points.  The PO needs to shift the whole curve down, so that instead of starting at 40 points for the release, it starts instead at 37.  Some automated tools may support this, but in a manual situation or where you’re tracking in Excel this can be a real pain in the neck and stuff that’s a pain in the neck ends up not getting done.

UPDATE: As commenter Nigel Thurlow points out, if you use Conservation of Points you must use a rolling average for velocity in Sprint Planning.  Using the single data point of “last sprint’s velocity” as your sprint planning velocity (rather than a rolling average) will leave you chasing bad data up and down the burndown chart, essentially amplifying the negative effects of unfinished stories.

Acknowledgements

Many thanks to Joe Justice of Wikispeed and my friends at GE Power and Water in Mumbai who inspired me to finally write this down.

 

 

 

 

 

 

 

About JR
Software guy, startup guy, non-fiction glutton, south shore inhabitant

One Response to Scrum Point Accounting for Unfinished Stories

  1. I couldn’t agree more. Having a stable burn-down also allows for direct investment in the Scrum backlog by VC.

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