Tuesday, April 17, 2012

Retrospective Velocity - Part 2 of 3

One of the key take away messages from the experts in the field of estimation is not to estimate at all.  To quote Steve McConnell: “ If you can’t count the answer directly, you should count something else and then compute the answer by using some sort of calibration data”.  So, if we can’t count our velocity directly we can count the number of bugs in our last project, how long they stayed open, how many requirements were present and so on.  Our calibration data is that all of those requirements and bugs took place in the time interval of the project.  It’s not especially fine grained but in a waterfall model we are not looking for fine grained data.

Some may argue that bug reports and requirements are not precisely defined and standardized.  What passes as a single requirement for one team might be 3-5 separate requirements for another team.  Some teams have bugs like “it doesn’t work” while others might enter a dozen or more particular bugs to cover the same underlying defect.  Here is the strange thing though: it doesn’t matter.

Just like story points are not standardized, all that matters is that within your team you tend to be consistent.   Whatever your team’s definition of a story point is if you’re doing Scrum is likely to represent about the same quantum of work next month that it represented last month.  In the waterfall world,  the level of granularity you bring to your bug reports is likely to be fairly constant.  The point to keep in mind is that we’re not looking to equate points or bug counts against anything but other points and other bug counts.  So, if your last several projects had 6 requirements, generated 60 bugs and took 6 months you have a velocity of 1 requirement and/or 10 bugs per month.  If you next project arrives with 15 requirements and a deadline of three months from now we can safely conclude that you are in trouble!

Keep in mind the distinction between accuracy and precision.   In the proceeding case we can say with high confidence that you are probably hosed.

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