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Monday, July 30, 2012

How does agile teams estimate the size of the project?

Agile teams separate estimates of size from estimates of duration. There are two measures of size:
1. Story points
2. Ideal time

Estimating Size with Story Points

- Story points are a relative measure of the size of a user story.
- A point value is assigned to each item when we estimate story points.
- Relative values are more important than raw values.
- A user story estimated as ten story points is twice as big, complex, or risky as a story estimated as five story points.
- A ten-point story is similarly half as big, complex or risky as a twenty-point story.
- The most important thing that matters are the relative values assigned to different stories.
- Velocity is a measure of a team's rate of progress per iteration.

- At the end of each iteration, a team can look at the stories they have completed and calculate their velocity by summing the story point estimates for each completed story.

- Story points are purely an estimate of the size of the work to be performed.
- The duration of a project is not estimated as much as it is derived by taking the total number of story points and dividing it by the velocity of the team.

There are two approaches to start with:
1. First Approach: Select a story that you think is one of the smallest story and say that story is estimated at one story point.
2. Second Approach: Select a story that seems somewhat medium and give it a number somewhere in the middle of the range you expect to use.

Estimating Size in Ideal Time

Ideal time and elapsed time are different. The reason for the difference, of course, is all the interruptions that may occur during any project.
- The amount of time a user story will take to develop can be more easily estimated in ideal days than in elapsed days.
- Estimating in elapsed days require us to consider all the interruptions that might occur while working on the story.
- If we instead estimate in ideal days, we consider only the amount of time the story will take.
- In this way, ideal days are an estimate of size, although less strictly so than story points.
- When estimating in ideal days, it is best to associate a single estimate with each user story.
- Rather than estimating that a user story will take 4 programmer days, 2 tester days, and 3 product owner days, it is better to sum those and say the story as a whole will take nine ideal days.

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