Story points and ideal time

A common misconception by teams is that there is a hard-and-fast relationship between story points and ideal time. They might devise a rule that says 1 story point = 8 ideal hours, which allows them to conclude that a story estimated at 3 story points will disaggregate into engineering tasks totalling 24 ideal hours.

Wrong! There is no relationship between story points and ideal time. During release planning, let's assume I estimated a user story at 3 story points. However, during iteration planning the total estimate for the associated engineering tasks came out at 28 ideal hours rather than 24. This is simply indicating that my initial estimate was out by approximately 14%. My best guess is that this underestimation applies to all the user stories in the iteration. This is what velocity and yesterday's weather are all about.

During release planning a team has an estimation error of a certain magnitude when they're looking at something far away. During iteration planning they have an estimation error of a different magnitude when they're looking close up.


Tags: agile, user stories

posted by Simon Baker @ permalink
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