I recently encountered the Stacey matrix in an answer by Stephan Weinhold. After looking at the linked image provided & doing a bit more reading that describes it as a way to characterize complexity, I thought of two specific use cases for agile software projects.
Case 1. Definition of ready & backlog grooming
Part of my definition of ready is "defined well enough to be scoped." A story with too much uncertainty, vagueness, or disagreement isn't ready because it is then unlikely to be successfully completed within a sprint.
Thus if we plot our backlog on a Stacey chart, we could use a defined area in the lower leftish as part of the definition of ready. (EDITED to clarify: I'm thinking of a region roughtly the size of the entire lower left quadrant here, not just the lower left corner. I imagine the boundary would be wide, and might well be asymmetric.)
Furthermore, a story's location outside this area indicates what kind of grooming needs to be done in order to get it into the ready state. Items that are vague or not agreed as to "what" require mostly stakeholder work to get more clarity or agreement. Items that are uncertain or not agreed as to "how" could benefit from more research or an exploratory spike.
Case 2. Complexity metric in place of story points
The best practice for story points, t shirt sizes, or similar relies on having a standard unit story so your team can do relative sizing. But that can be difficult for various reasons.
Since story points have also been described as a measure of complexity, and the Stacey matrix is about measuring complexity, why not define a scalar based on Stacey coordinates instead?
It could be a simple sqrt(x2 + y2), or a less rectilinear version that gives more weight to the "how" uncertainty than the "what", which is what I'm leaning towards.
So my questions are:
A. Has anyone done anything like this? How has it worked?
B. What problems might arise from this approach, either for case 1 or case 2?
The one thing that concerns me about case 2 (using a Stacey metric instead of story points) is that, although it captures complexity, it doesn't capture size. I'm thinking maybe an INVESTed story is already within a reasonable size range, though?
EDITED TO UPDATE: I've concluded that size needs to be its own metric, and am working with my team to define an objective, similarly ten point scale. I plan to record the three scores separately, and will then play with various combinations to see which seems to be the most consistent across sprints.
Thanks for any comments, feedback, or further reading!