Understanding Story Points in a Scrum Project
Posted on November 17th, 2009 in Agile by siddharta || No Comment
I’ve found that the concept of Story Points is one of the most confusing for people to understand. People are so used to estimating in real time – days and hours – that the abstract nature of story points is a bit hard to grasp. To make matters worse, there are different and sometimes contradictory ways of thinking about points. Here is how I think about story points
- Story points are a measure of size, not time or effort. This is a change in perspective for many teams since they are used to thinking in terms of real time. Here is an analogy to explain the difference: Suppose I ask “How long will it take to go from home to office tomorrow?” The answer is that is depends – depends on whether you take a car or bus, depends on the traffic and a host of other random factors. On the other hand, if I ask “What is the distance between home and office?” then the answer is a constant. No matter what the mode of transport or the traffic, the distance remains the same. Story points are like estimating the distance. They remain the same, no matter who is working on the story. The actual time taken may vary based on many factors. The person working on the story, meeting time, wasted time, all contribute to the actual time taken, but the size still remains the same.
- Story points are relative. In regular estimating you estimate in absolute units or days or hours. With story points you pick a reference story and measure everything relative to that. This works out better because people are better at relative comparisons. If I give you a box and ask the weight, it is difficult to estimate it very well. Given two boxes it is easier to say that one is double the weight of the other.
Whenever I get a question, I try to keep in mind: Story points are like estimating distance, and story points are relative. In a future post I’ll write about how this helps resolve some common questions.
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