Concept: As explained previously, the tight mathematical relationship between RTot and I/C$Tot limits how much the combination can tell us. The limitation becomes apparent when trying to make trade-offs. There, the necessary balance between R-tasks and I/C-tasks eliminates any real give-and-take.
As noted, the restriction conflicts with our intuitions: we feel that work done ahead (R-tasks) and work whose start is delayed (I/C-tasks) should be more independent than suggested by ES theory.
In this post, the intuitions are explored further, exposing a deeper conflict. Then, a resolution of the difficulties is proposed.
Practice: The dependency between RTot and I/C$Tot reflects dependency in the underlying data, specifically between R-tasks and I/C-tasks. The difficulty is not just with the practice of trade-offs but with the type of connection between the two sets of tasks.
Consider the implication of the following questions:
- Why think that the value delayed by impediments and constraints must be exactly the same as the value that’s
potentially delayed by rework? [1]
- Conversely, why should the amount of value that might require rework necessarily imply that an equal amount of value suffers from impediments and constraints?
The first question challenges the relationship from I/C to R. It implies that work done prematurely can just happen to occur, i.e., the connection between the two is contingent rather than necessary.[2] This seems to agree with experience. We often observe initial work being held back, but rarely think of rework as an effect of doing so.
The second question challenges the relationship from R to I/C. It implies that impediments and constraints can just happen to occur—they are not necessitated by rework. In our experience, we sometimes recognize that by working ahead, we use resources that might instead have been applied to other tasks. That, in turn, causes their start to be delayed. But, it seems that the relationship is contingent: surely, we can start work early without causing delay elsewhere.
What’s behind the intuitions evoked by these questions? The next post offers an answer and points to a way out of the deeper conflict.
Notes:
[1] The qualifier “potentially” is required because the amount of Rework is only a portion of the total value tied up in R-tasks.
[2] A contingent relationship is one which might or might not hold. A necessary one must hold. See Honderich, 1995, pp 608-10.
References:
Honderich, T. (1995). The Oxford Companion to Philosophy. Oxford: Oxford University Press.
Lipke, W. (2009). Schedule Adherence...A Useful Measure for Project Management. The Measurable News, Issue 3.
Lipke, W. (2012). Schedule Adherence and Rework. CrossTalk, November-December.
Lipke, W. (2011b) Schedule Adherence and Rework. PM World Today, July.
Lipke, W. (2011a) Schedule Adherence and Rework. The Measurable News, Issue 1 (corrected version). |
