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What works and what doesn't work in software development? For the first 10 years or so of my career, we followed a strict waterfall development model. Then in 2008 we started switching to an agile development model. In 2011 we added DevOps principles and practices. Our product team has also become increasingly global. This blog is about our successes and failures, and what we've learned along the way.



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Wednesday, March 3, 2010

Using Story Points for Sprint Planning?

Our team is still trying to get the hang of using story points. Until very recently, we weren't using them at all. I think this is for a few reasons:
  • Story points are relative to each other, not to the calendar. This makes them more abstract than person-days, so they're a little hard to wrap your head around at first.
  • We weren't in the habit of playing planning poker to put points on our stories. On the rare occasion we did put points onto stories, they were really just bastardized person-days (1 story point = 1 person-day).
  • Because we didn't have story points on things we had already completed, we couldn't use previously completed stories as a reference to put points onto new stories.
  • Because we didn't have any historical data on how many story points we closed in previous sprints, we had no idea what our velocity was, so we couldn't use story points or velocities to help plan the next release.
  • Story points aren't detailed enough for sprint planning. If you know that you have two weeks to code, and 3 people writing the code, how many story points can you commit to in the sprint? It doesn't have any meaning.

It's a vicious cycle: story points aren't useful if you haven't used them before... so people don't try to use them... so you don't gather the historical data to make them useful...

The problem is that we were spending too much time doing sizing estimates. As soon as you try to size something in terms of person-weeks, that implies that you have a pretty good idea what the low-level tasks are, and how long it will take to complete them. Honestly, it wouldn't be unusual for us to invest a person-week into sizing a story, when you consider how many people were pulled into each sizing effort for a few hours apiece. So we were told that we had to start using story points, and stop spending so much time on the sizing estimates. In planning poker, you rarely spend more than 2-3 minutes sizing a story.

People scoffed at the idea that you could plan a sprint without getting down to the task level and estimating how long it would take to implement each story, though.

Then someone found this article:
http://blog.mountaingoatsoftware.com/why-i-dont-use-story-points-for-sprint-planning

Now, I think we will be using story points for release planning (meaning, planning far into the future), and task hours/person-days for planning each individual sprint.

This means that we'll have to take a leap of faith. We have to start assigning points to stories before we start working on them. Once we've done that for a couple of sprints, we'll have some idea what our velocity is. Then we can start to use that information for planning at the release level. We'll see how it goes.

So, what does your team do with story points and sprint planning? Is it working?

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