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In John Stenbeck’s book “PMI-ACP and Certified Scrum Professional Exam Prep and Desk Reference”, he creates an “agile project management process grid” which describes 87 processes used in agile project management.   These processes are divided into five process groups (Initiate, Plan, Iterate, Control, and Close), which are analogous to the five process groups in traditional project management, and seven knowledge areas which can be mapped, more or less, onto the ten knowledge areas in traditional project management.

Today’s post is about the process 3.9 Sizing, which is part of the Adaptive Planning knowledge area.   When sorting out the various user stories that the development team is working on, there are two dimensions to be aware of.   The first dimension is that of “priority”, and the process of sorting out user stories based on priority is process 1.7 Prioritization.   The second dimension is that of “size”, and the process of sorting out user stories based on “size” is this process 3.9 Sizing.

First of all, what is “sizing”?   It is an agile estimating technique used to define the relative development effort required to complete user stories.   The word “relative” is important:   rather than saying “user story #5 will take five weeks”, you might say “user story #5 is a Medium user story,” if you use the sizing convention that is analogous to clothing sizes, namely, S, M, L, XL.

Here are the three units of measure a story’s size is usually specified with:

1. Ideal days–the work time required to complete an activity assuming there are no interruptions so that work can be completed with 100 efficiency.   The problem with using this absolute measure of work time is that different team members have different work experience, skills, and approaches to the work, so coming up with a “typical” or “average” speed for the team is difficult.
2. Actual days–the work time required to complete an activity assuming typical interruptions in the workplace that reduce efficiency from the theoretical 100% used to estimate “ideal days.”  Although this would seem to be an improvement on the “ideal days” measure, cataloguing all of the factors that reduce ideal days to actual days is difficulty, and prevent “actual days” from being a useful measure.
3. Story points–as opposed to the more “absolute” time estimates discussed in the two paragraphs above, “story points” are units of measure used to quantify the work effort and complexity required to develop a particular user story relative to other user stories.   They provide a relatively quick, high-level indicator of how difficult the development of any particular user story will be.

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