November 29, 2016
Story Points and Complexity
—Story points are more than just complexity.
In Story Points and Velocity, I reference Mike Cohn's book "Agile Estimating and Planning" and his view that story points are a relative estimate of the complexity, size or risk in a story.My software team and I moved away from estimates in man-days to story points. In doing so I placed a heavy emphasis on the relative aspect of story points and use a story point baseline to keep track of the relative measures created by the team for the stories they work on.
To move the team away from the notion of man-days I emphasized complexity as a means to measure stories. This worked for several months until people began to raise questions regarding what is complexity.
To being the discussion, I floated several perspective on story points. These included providing the team with the following documents.
- It's Effort, Not Complexity
- Story Points Are Still About Effort
- Estimating relative sizes (e.g. story points)
I included the last article because of its emphasis on the relative nature of story points and its comments on haggling over definitions of complexity. My prescience proved correct. We spent 30 minutes discussing the matter and ended the meeting with an agreement to revisit story costs during the retrospective. I failed to convince that it's the relative ranking of stories that are important to the velocity calculation.
In my description of story points I emphasized that the by selecting powers of 2 as our scale we need only agree that stories are twice or half as complex relative to the stories in our baseline.
I have a problem with relative costing using Fibonacci numbers because it's difficult for me to judge the difference between a 2, 3 and 5 point story. I am much more confident that halving or doubling the cost is an easier question to answer. If I run into a 3 point story I am happy to count it as a 4 and move on because I don't place an lot of emphasis on making "accurate" estimates.
I emphasized that it's not so much the number we are interested in, although you can't diminish its importance. I feel that the cost exercise is an important element of gaining consensus on what a story really encompasses. I tend to drive cost discussion using outliers. Not so much to rein in the costs but to ensure that the outliers explain their thinking and observations on a story and then build consensus on the cost.
Curiously, the story point baseline has proved invaluable. It ensures that simple questions can be asked about a story being costed. Those questions revolve around whether people are convinced that the cost of the story is like a story (or stories) in the baseline.
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