Relative Sizing of User Stories (Scrum)
- Tee-Shirt Sizes. For release planning we might use estimates of relative size. When less is known about the user stories (features or requirements) for a release, we can estimate using a broad brush approach. Based on such criteria as how complex we think the user story is, how much effort it will take, and the unknowns or doubt, we give it a tee-shirt size (XS, S, M, L, XL). We can then compare all the user stories and assign relative sizes. For example, we can take one user story and based on the above criteria assign it a tee-shirt size of “Large.” We can then compare all the other stories against this “Large” size and assign the relative value of each story. This relative size estimating can help the product owner (business representative) decide which user stories to prioritize for a release.
- Story points. We can then assign each tee-shirt size story points based on an arbitrary scale, such as the Fibonacci number sequence (1, 2. 3, 5, 8, 13, 21…). If a user story is Medium, for example, we might assign 8 story points. If Large, 13. We can then translate the tee-shirt size of all the user stories into story points. It’s important to remember that these story points are still relative. It really doesn’t matter if a Small is 2 or 3 points, as long as it’s consistently applied.
Relative Sizing of Projects, Phases, Deliverables, Tasks (Waterfall)
For years we have used relative size estimates on traditional projects. I have found this most effective when actuals have been collected over enough time to have confidence in the numbers. While I have only used relative sizing on deliverables (such as a small, medium, or large report), I know of teams that have used them on the whole project, project phases and tasks. As with Scrum, we usually base traditional relative sizes on complexity, effort, and doubt (risk), as well as on the history.
Round 1: Scrum wins, but it’s not a knock-out.
In my experience using relative sizes on traditional projects is often done to short-change the planning process. With Scrum the relative size of the user story actually gets refined as it approaches the sprint in which it gets delivered. While some traditional teams have the discipline to refine the estimates (as a project manager, I always encouraged it), many more give in to management’s pushback about not changing the date, scope, or cost. Scrum processes, by their nature, encourage change and refinement; traditional processes do not always do so.
Scrum Planning Using Delphi (Planning Poker)
Planning Poker uses a kind of Delphi technique to reach consensus on the relative size of the user stories. Each person on the delivery team (but not the product owner) uses a special “deck of cards,” which can be an actual deck or pieces of paper. Each card has a number. If using the Fibonacci scale, the deck would have cards, each containing a number in the scale (1, 2, 3, 5, 8, 13, 21, etc.) going as high as desired. The product owner explains the details of the user story and at the count of three, team members turn over the card with the points they think most appropriate. For example, two team members turn over a 3, one a 5, two an eight, and one a 21. They discuss their reasons for “playing” their cards. Then at the count of three they turn over a card, the same or different from the previous round. Again, they explain their rationale. This process continues until consensus is reached.
Traditional Planning Using Delphi
The Delphi technique involves a group of experts providing their estimates anonymously. Like planning, poker, there are rounds. The experts provide their estimates anonymously. A neutral party collects the estimates, shuffles them, and silently reveals them to everyone at the same time. No discussion is supposed to occur. Rounds continue until consensus is reached.
On traditional projects I have tried using Delphi anonymously only once. It didn’t work. I have found the real power of Delphi is in the discussion of each person’s assumptions about the estimates, so as a project manager, I modified Delphi to allow discussions between rounds.
Round 2: Scrum wins, but again it’s not a knock-out. I love the Delphi technique. I love having the team reach consensus on estimates, whether traditionally or through planning poker. It provides team accountability for the estimate, and increases the chance of team and individual commitment rather than compliance. So what difference does it make whether traditional Delphi or planning poker is used? Everyone can understand planning poker. I have seen teams take to this technique immediately. So while Scrum makes things easy and practical, the traditional Delphi, including its name, feels arcane.
So, the current score is two zip. But the match is not over. Much more to come…
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