Sunday, January 23, 2011

Why Story Points should be abstract units?

Imagine that you assumed that 1 story point is about 4 ideal hours of work and you made all the estimations according to that assumption. When the sprint finished you divided a sum of story points of done stories by a number of spent hours and the result was that 1 story point is 6 hours. So how to proceed during the next sprint planning? If we assume that 1 story point is now 6 hours, we estimate stories in a different way than before. In other hand, keeping in mind that 1 story point is 4 hours, although we know that last sprint it was 6 hours is also confusing. In the described case 1 story point corresponds to some certain time, so it looses its real meaning.

Story points should be some abstract units expressing relations between stories in a way a team asses them. When they are abstract there is no other way to estimate a story than by comparing it to already estimated stories. Thanks to that, estimating is always the same, there is no confusion.

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