Concepts on Estimating
- Agile teams acknowledge that we cannot eliminate uncertainty from estimates, but they embrace the idea that small efforts are rewarded with big gains.
- Agile teams can produce more reliable plans because they frequently deliver small increments of fully working, tested, integrated code.
- Agile teams do not rely on single expert to estimate. Estimates are best derived collectively by the team.
- Estimates should be on a predefined scale.
- Features that will be worked on in the near future and that need fairly reliable estimates should be made small enough that they can be estimated on a non-linear scale from 1 to 10 such as 1,2,3,5, and 8 or 1,2,4, and 8.
- Larger features that will most likely not be implemented in the next few iterations can be left larger and estimated in units such as 13,20,40, and 100.
- Some teams choose to include 0 in their estimation scales.
Four common techniques for estimating are:
1. Expert Opinion
- In this approach, an expert is asked how long something will take or how big it will be.
- The expert relies on his/her intuition or gut feel and provides an estimate.
- This approach is less useful on agile projects as compared to traditional projects.
- In an agile project, estimations are made on user stories or other user-valued functionality. It requires lot of skills by more than one person which makes it difficult to find suitable experts.
- Benefit of expert opinion is that it does not take very long.
- In this approach, the estimator compares the story being estimated with one or more other stories.
- If story is twice the size, it is given estimate twice as large.
- You do not compare all stories against a single baseline, instead, each story is estimated against an assortment of those that have already been estimated.
3. Dis aggregation
- It refers to breaking a story or feature into smaller, easier to estimate pieces.
- Be careful not to go very far with this approach.
4. A fun and effective way of combining these is planning poker.
- In planning poker, each estimator is given a deck of cards with a valid estimate shown on each card.
- A feature is discussed, and each estimator selects the card that represents his or her estimate.
- All cards are shown at the same time.
- The estimates are discussed and the process repeated until agreement on the estimate is agreed.