Agile Estimation in Practice

The longer I spend working as an agile coach, the more I find myself in disagreement with Hamlet. To estimate, or not to estimate? That is the question. Out of all of the agile practices which have been adopted in recent years, few have proven more controversial than this one. The battle for and against rages like Shakespearean armies set against each other's teeth.

At first blush there doesn't seem to be any reasonable cause for disagreement. The rationale for making estimates is ostensibly straightforward. If a team is to work in Sprints, and to deliver something at the end of each one, then the work must surely be estimated. Otherwise how can the team know if it is even possible to do the work within the Sprint? How can they commit to deliver something by the end of that time-box if the effort involved is of uncertain magnitude?

Well, there are two things that we need to draw out at this point. Firstly, the above rationale assumes that Sprints will be used, and that delivery will therefore be time-boxed. That's a very Scrum oriented philosophy...but Scrum isn't the only agile way of working. Lean-Kanban teams, for example, don't use Sprints and rarely make use of estimates. Secondly, Scrum itself says nothing about estimation. It only says that each item in a backlog must be sized - how that sizing happens is up to the team. It should also be remembered that a Scrum team commits to a Sprint Goal that delivers value, not to the delivery of a certain number of estimated points.

So then...to estimate, or not to estimate? Let's listen in at the camp-fires of each side, and pick out in more detail the arguments they make for and against.

For (Ye Scrum Brigade of Sprinte and Stande-uppe)

• "Estimates allow us to predict when a Sprint Goal will be met, and therefore when a substantial increment of value will be delivered"

• "Our estimates help our stakeholders plan ahead. They are part of the value we provide" 

• "Estimates help us to de-risk scope of uncertain size and complexity"

• "Estimated work can be traded in and out of scope for other work of similar size. Without estimates you can't trade"

• "The very process of estimation adds value. When we estimate we discuss requirements in more detail, and gain a better understanding of what is needed"

Against (Ye Lean Kanban Brigade of Boarde Pullers)

• "Estimates are rarely accurate. All you are doing when you estimate a piece of work is to set false expectations"

• "In practice, estimation is seen as a commitment, not as a best guess. Every time you make an estimate, you make a rod for your own back"

• "Estimation is time consuming. The time a team spends playing planning poker or whatever is time that could have been spent on delivery. Estimation is waste."

• "It's the actuals that matter, not estimates. Agility requires metrics, and the only metrics that count are those that reflect actual delivery"

Both sides are right

If you see this debate in terms of whether a Scrum or Lean-Kanban process is being followed, then both sides are right. A Scrum process is optimized for project work where scope risk is high and an entire system is represented. The requirements tend to be uncertain, complex, and very heavily intertwined. By committing to a Sprint Goal and to the delivery of a substantial increment of value, that risk can be managed. Uncertain and interdependent requirements are batched together into a Sprint and dealt with as a group. When this is done well, you have a clear Sprint Goal and a coherent Sprint Backlog. When it is done badly, you have a vague or disjointed Sprint Goal, a mishmash of requirements that command no sense of team purpose, and no team commitment towards the delivery of an increment.

A Lean-Kanban process, on the other hand, is usually focused on "Business As Usual" (BAU) activities. The diet of a Lean-Kanban operation should consist of small and repeatable changes. They don't have to be related at all...in fact they shouldn't be. Things like bug fixes, minor enhancements, and administrative tasks are representative of this kind of work. Scope risk is low because the process of making such changes is well understood. Estimates are generally held to be unnecessary because there is very little uncertainty to deal with. There is no need for work to be batched...each change can be actioned and delivered independently of all others. Work is enqueued and actioned according to priority and the required quality of service. Predictions are based on the actual rate of delivery, not on estimates. In a Lean-Kanban way of working, the actuals are indeed everything.

Methods of estimation

So then, estimates add value where scope is uncertain and there are associated risks to be managed. That's why Scrum teams engaged on projects typically make use of them, but Lean-Kanban BAU teams generally don't. Now let's look at three simple methods of estimation that Scrum teams, or other teams doing project work, can make use of.

Planning Poker

This is a well established technique popularised by Mike Cohn, and variations on his Planning Poker cards can be found in offices across the world. A typical Planning Poker set has cards with the following numbers: ½ 1 2 3 5 8 13 20 40 100. Nerds will observe and be irritated by the fact that this is roughly (but not quite) in line with the Fibonacci sequence. Here's how it's played:

• An identical hand of cards is given to each team member. Each team member will have a set of cards with numbers on the above pseudo-Fibonacci scale.

• The Product Owner describes the piece of work to be estimated. Normally this is a user story with acceptance criteria.

• Each team member mentally estimates the size of it on the scale. They can ask the Product Owner questions to clarify any points, but for the moment they will keep their estimate to themselves.

• Each team member places the card that corresponds to their mental estimate face down in front of them.

• At the facilitators instruction - usually the Scrum Master - the team turn their cards over. In an ideal case the cards will all have the same value, suggesting that the team have a common understanding of the requirements and the likely effort that will be involved.

• If the values are different, the team then need to discuss their estimates and their reasoning behind them. They need to understand each other’s thinking, and from that reach a consensus. It may be necessary to replay the cards several times before agreement is reached.

• By convention, estimates are written on the corner of a User Story card before being placed on a Scrum board.