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.
Wednesday, 10 November 2004
Story points and ideal time
Posted by Simon Baker - Permalink
