A wrong emphasis on task estimation

Kai — Sun, 03 Aug 2008 13:01:30 +0000

From discussions over the last few months i realized that quite a lot of agile teams have a high emphasis on task estimation. So far i am very much in doubt of the benefits task estimations will give to a team. In fact i come to believe that a high emphasis on task estimation will do more harm than good and is the first step into micromanagement. Especially if your team does full blown task estimation including reporting on time spent on task and estimating the time remaining. That does not mean teams shouldn’t do task estimations but they should have a clear idea why they are doing it and what they want to get out of it. Teams usually try to get out two things from task estimation: capacity (velocity) of the team and tracking iterations (eg. iteration burn down charts). But both things can be achieved by other agile concepts which an agile team (should) apply anyways: velocity through story estimation and iteration tracking through a physical story wall. Hence it is questionable if task estimation is needed at all.
Deriving team velocity out of task estimation is very dangerous and gives a wrong impression of real velocity over all iterations. The concept of velocity only works if the team sticks with the initial estimates and has a common base line and scale for all iterations. Estimating in time does not give the team a common base line regardless if the team uses hours, days or ideal days. What is an ideal day? Did i really spend the same amount of hours for the last four-hour-task? How do i take pairing or pair swapping into account? Estimating in time is flawed and is raising many questions as people interpret time quite differently.
In addition there is a hidden effect when estimating with time. As the team progresses through the project it acquires more and more knowledge. This knowledge is reflected in better estimates which is of course positive. But it also means that velocity from iteration N is not comparable with iteration N-1 because there is no common base line. What is achievable in one ideal day/hour shifts with the increasing knowledge of the team. This effect does not happen if estimation is done relatively and the team sticks to the base line from the first estimation session of the project. Estimation still gets more accurate with gained knowledge but with a relative scale a task will be inserted more accurately within this scale.
Would it help to estimate your tasks relatively by size like stories (and call it gummy bear points)? It might work if you stick to the base line you created in your first iteration. A one gummy bear point task from iteration one is always the same size as a one gummy bear point task from any other iteration. I’ve never been on a team where tasks were estimated relatively so i can’t really tell if this approach would work.
The other purpose of task estimation is tracking the progress of an iteration. Though it is important to track iteration progress it is much more important to track project progress. A completed story is the unit that delivers value to the product. Hence the focus should be to find out how much stories a team can finish in one iteration instead of tasks (the real velocity). Tracking completed stories on a project scale (via a story burn down chart) together with story velocity will give a team the ability to predict the projects end date. Task estimation simply fails to add visibility of progress on a project scale. Don’t get me wrong here. I still think that breaking down stories into tasks in iteration planning can still be valuable. But why putting in the extra effort to estimate tasks when the stories are already estimated? Especially if the team operates in short (and prefered) two week iterations.
A key success factor for task estimation to become redundant is to follow the INVEST principle for all stories by heart. Teams can introduce N-1 analysis iterations to have stories as close as possible to INVEST before they are played in an iteration.
For iteration tracking a physical story wall including all current tasks is absolutely sufficient. With a short look every team member can see if progress of the current iteration is healthy or not.
One very bad thing i experienced when emphasizing to much on tasks is that the team loses sight of stories as a whole. Particularly if tasks are split into the horizontal architectural layers of the software. There is a high risk that integration problems will arise and tasks will bounce more often between “test ready” and “testing failed” then they need to. Every team member should understand the vertical slice of the system which the story represents and see it as a whole.

I strongly believe we can live very well without task estimation in agile projects. Most of the estimation effort should be put into story estimation to enable project tracking. Thus in alignment to the pattern of the agile manifesto:

Project and story tracking over iteration and task tracking

Kai Ramuenke » Estimation

A wrong emphasis on task estimation