Story pointsStory points are a method to size a piece of work without having to get bogged down in how long it will take. Let's say the story is "Filling a glass of Orange Juice".
- Time based approach: how long will it take to pour a glass of orange juice?
- Story points approach: "let's estimate what size the glass is".
With both approaches you have inaccuracies. The first might incorrectly estimate the speed of the pour, while the second might not size the glass correctly. But the reason we moved away from a time based approach is due to developers inability to provide accurate time estimates, we just seem to be better at sizing something as opposed to giving it a time estimation. You've all heard different equations for estimating a story or task length - take a developers estimate and double it, or even multiply it by 2.5. We are notorious underestimaters even given this knowledge! Points based estimates are supposed to fix this because you estimate the size or complexity of the story instead. The theory is it's easier to estimate roughly how big a glass of orange juice is than to estimate roughly how long it takes to fill.
Also, some developers are faster than others. So if you quote a glass of orange filling at 2 days, it might take a junior developer 3 or 4 days to do the same story. If we had it estimated in points then that solves the problem. 2 points to a junior developer can mean a different thing to a senior developer and we can account for that by giving the junior devs (as a resource) a lower sprint velocity. If we lose them from the sprint then it's easier to account for what the loss in points will be.
This sounds fantastic, but doesn't work quite as awesome as you'd think. You've been in those planning meetings where the developers are thinking about a story, prodding the BAs for answers and eventually come to their conclusion. They all raise their cards and the points average out at 5. BAs and project managers shout "How on earth can that be a 5 point story?!?". This completely misses a couple of points of what the estimate is. It's a story size, as in agreement by the developers. What exactly is 5 points anyway? It's just a number that defines story complexity. But quite often you'll get argued down and the story ends up being 3 points. And suddenly you have your 50 point sprint full of underestimated stories and only complete 75% of the sprint. It's almost like the reverse of the stereotypical developer estimates happens, developers give their estimates and rather than the old school "double it!" we get a "half it!" approach.
There are more problems than this, but is better thought of in terms of Velocity.
VelocityAs I said, what exactly are story points anyway? And what exactly is velocity? To give you an idea of the misconceptions I have witnessed I will paraphrase a statement I head in a recent project I was involved in:
'We should have a velocity of 50 points per sprint.'
This instantly rose suspicion with me as we hadn't even hit 3 sprints and were actually performing a little lower than that. It's also a remark usually associated with a misunderstanding of what points and velocity means. I poked about with a few questions and eventually discover that the reason the sprints should have a 50 point velocity is due to another similar-ish project in the company that had a 50 point velocity.
So, let's look at the question again, what exactly are story points anyway? Let's go back to our story "Filling a glass of Orange Juice":
- Team A estimate this as 5 points
- Team B estimate this as 3 points
- Team C estimate this as 8 points
- Team A fill the glass of orange juice. It takes them 2 days (it was a very big glass!).
- Team B, also start to fill a glass of orange juice. It also takes them 2 days even though they pointed it lower!
- Team C fills their glass. Add a dash of mango to it because they have a pretentious client and then paint some fancy designs on the glass. They were probably right to point it at 8
There's 2 things I'm trying to get across here.
- Firstly Team A and B quoted different points for what was effectively the same complexity of work. This really doesn't matter. I would expect Team B to also maintain a lower velocity, but that doesn't mean they actually produce any less work. They will have the same output, they just estimate and process points at a different rate.
- Also, look at Team C versus the other 2 first. Although a story might seem like the same piece of work sometimes it's not. It can depend on technology, who your developers are, etc.
Effectively, as far as different projects are concerned velocity is only relevant to that project. You shouldn't try to impose another projects velocity (or even points) on another independent project.
Up until this point I can actually work with all the concepts. The issue I have with points and velocity is a misunderstanding of the concept as opposed to something more fundamental. But I would add that I'm frustrated of having to re-educate people every time I join a new agile project.
SprintsSprints are something I have really become less fond of as time has elapsed. Taking a look at the definition of a sprint on the face of it all they seem like a good idea (taken from wikipedia):
'A sprint (or iteration) is the basic unit of development in Scrum. The sprint is a "timeboxed" effort; that is, it is restricted to a specific duration. The duration is fixed in advance for each sprint and is normally between one week and one month, although two weeks is typical.
'Each sprint is started by a planning meeting, where the tasks for the sprint are identified and an estimated commitment for the sprint goal is made, and ended by a sprint review-and-retrospective meeting, where the progress is reviewed and lessons for the next sprint are identified.
'Scrum emphasizes working product at the end of the Sprint that is really "done"; in the case of software, this means a system that is integrated, fully tested, end-user documented, and potentially shippable.'
- Story commitment
- Shippable product
My first issue is this, if you're going to "timebox" the work you are presuming that every single deliverable can be developed in your timeboxed period. In every project I have worked on to date about 10% of the sprints have truly delivered something shippable. Most sprints finish with incomplete stories being moved into following sprints, or partially delivered features due to your sprint periods being over-restrictive.
My second issue is with the commitment to sprint tasks/stories. Generally, when the sprint content has been defined or stories "accepted" into the sprint, you're not really supposed to change it. We all throw this concept out fairly early, because that's the first bit that really breaks agile. The reason behind not being allowed to change the sprint when it has already started is you'd never get any work done if people kept changing the stories and work from beneath your feet. But there has to be some kind of flexibility here. Priorities change frequently in fast moving projects so you frequently have to move stuff in and out. This means you have to either:
- Estimate not just stories that can fit in a sprint, but above and beyond that
- Or estimate new stories as and when we need to push stuff in and out of sprints
Now when the new stories that come in... do they "fit" with our deliverable? Maybe they do, maybe they don't. Either way, to be truly agile we really should allow priorities to change and allow work to get completed when it's needed. But we are dancing a fine line with our shippable product here!
Which takes me on to my final issue - the "Potentially shippable product". Sprints don't help this, they hinder it. What you end up doing is shoehorning X points worth of stories into a sprint and calling it your "shippable" piece of work. When really what you frequently end up delivering is partially complete features that no end user would really want to use (yet).
Alternative?While writing this post I came across this blog post Stop using story points. Looks like I'm not the only one frustrated with this, and I'm a little late to the game! I have to say I love the concept of estimating in Apples and Oranges. I also love the idea of variable length iterations. I wish I could claim that idea, but alas I cannot!
Flexible iterations is probably the alternative I will seek from here on. One of the biggest advantages is you can define what you're going to ship rather than allowing your iteration to define this for you. Pick something small and manageable, like 2 or 3 features (depending on your feature sizes) that will complete a few pages, or give you a functional service. This doesn't mean you have to stop using points. If this is something you're already comfortable with then keep using them. You can also still calculate velocity, but maybe create a "weekly" velocity so that you can easily calculate your iteration lengths. But the point is pick something shippable you will complete and then estimate the iteration.
Basically, what I'm suggesting is, let's get back to being agile. Let's not taint such a great methodology with unagile practices and in result giving it a bad name.