Would you wear a shirt that was too small?
Of course not, it would look ridiculous! The same attitude should apply when estimating effort to complete a project.
Estimation can prove a tricky thing for teams to master and this is particularly true of multidisciplinary, short-term project teams.
Estimation is a collaborative team effort and can take many attempts to produce accurate and realistic results. The team must build a shared understanding of complexity and effort. Story points are the recommended measure of complexity, risk and effort, the higher the number, the more complex, risky and/or time consuming a Story.
The Fibonacci sequence is commonly used for story point estimation, a sample sequence is as follows: 1,1,2,3,5,8,13,21,34; the pattern can clearly be seen; each number is the sum of the previous 2 numbers. This sequence allows us to plan for large or uncertain stories by assigning an appropriate number from the sequence. A small simple story would be assigned the value of 1, all subsequent stories are then examined to determine their point value when compared to the complexity of previously pointed work items.
Implementing Story points can prove quite difficult as it requires time to build a shared understanding of the effort,complexity and risk involved for each item. The importance of estimation however means that it must be done and in a way that makes sense to the team members. Alternative estimation techniques can be implemented effectively and work well as a stepping-stone to Story Points. Simple estimation techniques work particularly well in the case of newly formed or short-term project teams. T-shirt Size estimation is an example of a technique which can be introduced before moving to Story Points.
It is easier for multidisciplinary teams to visualize their stories in terms of T-shirt Sizes. Estimation is based on the time, associated risk and complexity of implementation. The team members then pick a T-shirt size based on the risk and complexity assessment. T-shirt Sizes offer bands (2–3 days, up to 5 days) to allow for additional risk management and to offer a buffer in the case of underestimation. Underestimation happens frequently within project teams with members not only underestimating stories but also underestimating non-project related demands on their time.
The Extra Small or XS, is assigned to a very simple, well understood story which is easy to implement and should take less than a half a day.
Small or S, refer to stories which are also well understood, containing little risk but require additional effort to implement.
A story assigned a Medium or M, has an iteration allocation of up to 3 days. These stories usually involve more risk than XS or S, elements of uncertainty have been highlighted during planning which requires additional time for research around implementation. They can also have little risk but require a lot of effort to implement, possibly requiring team member collaboration to complete.
Large estimations are reached using the same assessment criteria as Medium, having discussed the story during planning the team may highlight additional risk in implementation or a multidisciplinary approach to completion. The additional risk or effort needed to complete a large story would require it be allocated up to 5 days in an iteration.
Extra Large or XL stories carry a large amount of risk and uncertainty, it is very unwise to bring a story into your iteration which will take the full cycle to complete. If a story is this uncertain or complex it means that we have a flawed understanding of its purpose and the steps to complete it. An XL should be discussed further to reduce ambiguity around implementation, with a better understanding it is almost always possible to break this story down into smaller stories (2 Large + 1 Medium) some of which can then be taken into an iteration and completed successfully in one cycle.
The benefit of using T-Shirt sizes is that it is a visual representation of the effort involved and team members more easily identify stories which are larger than others by asking, “would that story fit that T-Shirt?”. Asking this question in every planning session enables the team to become more comfortable visualizing and estimating the relative risk and effort of each story. Outside risks can also be considered when estimating, a story which may take up to one day to complete (Small) might become a Medium (up to 3 days) to allow for additional commitments (Training, Conference, Client Sessions) in a given iteration.
Estimation allows a team to gain insight into all stories planned for their next iteration, creating team alignment from the planning stage. Risks and dependencies are understood by all members and the team work towards a well understood, planned iteration goal. Correctly identifying risk and estimating accordingly has a massive impact on the success or failure of any project.
So, the next time your team sit down to plan, remember to ask, “What size t-shirt would this Story wear?”.
Top Tips for getting started;
1. Print a large estimation poster (see above) for your team planning session.
2. Get the team to re-point previous iteration work items to get a feel for their scale.
3. Identify stories to be estimated
4. Read through the detail of the story
5. Allow each team member to estimate a size for each Story;
a. If there is consensus across the team the story is assigned this T-Shirt size.
b. If there is mixed evaluation on the Story, the persons with the lowest and highest estimates will explain their reasoning before the team estimates again. (repeat until a consensus or team majority is reached).
6. Once the T-Shirt size has been identified, assign the top band value to the Story, (example, a Medium story with a band of 5–15, would be assigned 15 points).
7. Over several iterations, a team velocity will emerge, this will offer clarity to the Development Team and help them plan iterations effectively. It will also help the Project Management team to create release plan estimates.
