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Simulating a Project by Resampling Velocity

by Mike Cohn, 25 September 2011 | Agile Estimating

This post is from Mike Cohn's Blog - Succeeding With Agile® by Mike Cohn. Click here to see the original post in full.

I normally write about a new technique only after I’ve used it for a couple of years and have found it successful in a couple of different contexts. In this post I want to share something just such a technique. It’s a statistical technique called “resampling” that I’ve become quite fond of for making predictions about future velocity.

Resampling is based on the idea that things we’ll observe in the future will be similar to the things we’ve observed in the past. In the examples we’ll look at we’re saying that the velocities a team will see in the future will be similar to ones that occurred in the past. Resampling works by imagining we’ve put all old sample velocities into a bag. If we have past velocities of 18, 17, 18, 19, 22, and 20 imagine each of those written on separate slips of paper and dropped into a bag. Note that we’ll have two slips of paper with “18″ because our team here had that velocity twice.

To predict future velocity we reach into the bag and pull out one piece of paper. What’s written on it is our prediction of velocity in the first sprint. To predict the team’s velocity in the second sprint, we reach into the bag and pull out another slip of paper. But, before we do that, it’s important that we put the first slip of paper back into the bag. This is called “resampling with replacement.” We want to replace because for any given sprint the team is equally likely to get any of their...

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