Story points and ideal days are both techniques for estimating the size of work in agile software development. Story points are relative units that measure size, while ideal days estimate the time to complete a task if there were no interruptions. Velocity, the rate at which a team completes points, helps correct estimation errors over time. While ideal days are initially easier to estimate, story points drive better collaboration and don't decay over time. The document discusses factors to consider when choosing an estimation approach.

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2.  Estimating Size with Story Points
 Estimating in Ideal Days
 Techniques for Estimating
 Choosing between Story Points and Ideal
Days
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3.  Story Points Are Relative
› Story points are a unit of measure for expressing
the overall size of a user story, feature, or other
piece of work.
› Get Started with smallest or medium user story.
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4.  Velocity
› Is a measure of a team’s rate of progress.
› Velocity Corrects Estimation Errors.
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5.  Ideal time vs. Duration.
 Ideal Time and Software Development.
› The story being estimated is the only thing you’ll work on.
› Everything you need will be on hand when you start.
› There will be no interruptions.
 Ideal Days as a Measure of Size.
 One Estimate, Not Many.
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6.  Estimate Accuracy vs. Effort
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7.  Estimates Are Shared
› estimates are best derived collaboratively by the
team, which includes those who will do the work.
There are two reasons for this.
 The Estimation Scale
› “1, 2, 3, 5, and 8” or “1, 2, 4, and 8”.
› Could include “0”.
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8.  Deriving an Estimate
› Expert opinion
› Analogy
› Disaggregation
 Planning Poker
› Smaller Sessions
› When to Play Planning Poker
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9.  Considerations Favoring Story Points
› Story points help drive cross-functional
behavior.
› Story-point estimates do not decay.
› Story points are a pure measure of size.
› Estimating in story points typically is faster.
› My ideal days are not your ideal days.
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10.  Considerations Favoring Ideal Days
› Ideal days are easier to explain outside the
team.
› Ideal days are easier to estimate at first.
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11.  Agile Estimating and Planning by Mike
Cohn.
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