Bertrand Russell once gave a lecture on astronomy, and how the earth rotates around the sun, and how the solar system is part of a vast galaxy, etc and so forth… At one point he was interrupted by an old lady, or so the story goes, who said “What you’re saying is rubbish, the world is a flat plate resting on the back of a giant turtle”. When Bertrand Russell questioned her as to what’s below the turtle, she replied “Another turtle”. Bertrand persisted with “And what’s below that turtle then?” to which the lady replied “It’s no use – it’s turtles all the way down!”
I was reminded of this story recently when I was in discussion with a colleague about sprint planning. My colleague was explaining to me that they use story points for sizing and estimating stories, but they then break their sprint stories down into smaller tasks and use hours to estimate these tasks, rather than continue to use points.
I had never come across this particular practice before. Of course, I’ve seen teams who do everything in hours, I’ve just never worked with a team which used both points and hours. I’ve always worked in points for story sizing, and when the stories need breaking down, I would break them down into smaller points: It’s points all the way down! I’ve never had any problems with this approach, so I was curious as to the advantage of switching to hours.
My first port of call, as always, was Google. When that came up empty I turned to Twitter, and got a friendly response from none other than Mike Cohn.
— Mike Cohn (@mikewcohn) July 19, 2013
Now, I never thought I’d find myself disagreeing with Mike Cohn, indeed his book “Succeeding With Agile” has been something of a bible for me for the last few years, but on this issue I am still not convinced.
Mike has written a really interesting blog post on why he uses hours rather than story points for sprint planning (you can find it here). One of his reasons is because he feels hours are better short-term measure than points. In some circumstances I would agree with him (perhaps if your stories are MASSIVE, and you need to break them down into much smaller tasks), but in my experience it doesn’t generally appear to hold true. I use points for both stories and tasks – the only difference is that when we get around to task estimation & sizing, we expect to be a little more accurate than when we estimated the stories in the product backlog. Quite often we will take a story of say 5 points, and break that down into two 3 point tasks. So 3 + 3 doesn’t add up to 5. Who cares? the 5 was an estimate anyway, and I always push to make everyone understand that estimates are just guesses, and the further out we make the estimate, the more approximate it’s going to be. By the time we get around to doing our sprint planning i expect us to take a much deeper look into these stories, and benefit from additional analysis, so naturally I expect our estimate to change.
I usually do everything I can to steer away from hours, because it can often be too confusing for people outside of the team to understand why the total hours don’t add up to the total available resource hours. I’d rather just not have this conversation sometimes! Also, after explaining to everyone the key benefits and purpose of using points, I can imagine they’d be confused as to why we were suddenly ditching all the advantages of points, and switching back to hours for the sprint planning. By the way, I’ve covered the reason why we use points over hours in my previous blog post here.
Anyway, I just thought I’d write this post to show that both approaches are common, and I guess it’s just a matter of “whatever works best for you”. But I’m still not convinced with the whole hours thing!