Estimation, Wideband Delphi, and the Cone of Uncertainty

John Boal — Thu, 11 Dec 2008 04:13:41 GMT

After some training in the estimation technique of Wideband Delphi, I have tried it out in a real project/team environment. I think it was an interesting result, but as a single data point so far, I would hesitate to assess the tool as a success or failure. I will be curious to see how the estimate tracks to actuals for the feature... The use of Wideband Delphi in the initial stages of a project may be a good tool for rough sizing of features or whole feature areas. I am a bit leery of assigning "hours" [ideal hours] to estimates at this very high level of granularity though. Sometimes hours find their way to get turned in to schedules... and ideal hours are even more dangerous as they aren't fully loaded.

The cone of uncertainty is a nice principle that I think might perhaps need more airtime. (Not being a project manager, its a new one on me...) It states that at the beginning of a project, when the least is known, the estimation error can vary from .25X to 4X (not sure where these numbers came from). And as we move toward project completion, the estimation curve shrinks on both sides exponentially to approach 1 at project completion. For more information see the cone of uncertainty link.

However, as the "cone" narrows and we are a bit more certain of what it is we need to deliver, I still think the planning poker type of consensus estimation is more appropriate. It seems a bit lighter weight and much quicker for estimation. Granted, however that planning poker is a tool to be used at the story level (and estimates in points NOT hours), it might not do as well as the WD estimation at earlier stages. It is a similar process, but seems to be a faster implementation.

WD could be a useful tool for backlog prioritization and even perhaps story generation. I am not sure how valuable estimates from WD might be other than to help prioritize (in size and cost) less-well-known things in the product backlog. I still think that the planning poker is appropriate at the sprint and story level though, rather than WD. Another thing that strikes me as different is that WD doesn't necessarily engage the whole team doing the work - only "experts." I like to have the entire team exposed to the information and the planning, even if team members don't have much value to add to estimation at that phase. In my opinion, it helps with information sharing, project background, and overall depth of understanding.

Use the right tool for the right job I always say. I carry four screwdrivers in my toolbelt, two sizes of flat blades, and two sizes of phillips... Use a tool for its intended purpose. Watch out for trying to get too much out of estimation at an early phase, and definitely involve the team - they are going to be the ones who help the project actually come to fruition.

Bits 'n Widgets - Estimation

Estimation, Wideband Delphi, and the Cone of Uncertainty