Concept: In posts thus far, RTot and I/C$Tot have been treated separately. The assumption is that, if either one trips an alarm, action is required.
It is also possible to take RTot and I/C$Tot together. Doing so provides insights not otherwise available, but doing so also reveals limitations not otherwise visible.
Practice: When taken together, RTot and I/C$Tot offer new insights into schedule performance. Some of the key insights follow.
Together, RTot and I/C$Tot express the overall impact of late delivery, even though they represent two different senses of being “late”.
- RTot represents delay in the ultimate fulfillment of value: if work must be performed again to achieve the same value, there is a delay. [1]
- I/C$Tot represents delay in the initial delivery of value: it’s not that the same value is earned over again, but that the initial value is missing altogether. It will be delivered (if ever) only later than the originally scheduled time.
In both cases, the planned value is finally achieved after the ES time, and in that sense, both RTot and I/C$Tot represent the impact of being late.
Jointly, RTot and I/C$Tot provide a balanced perspective on schedule noncompliance.
- For rework, it is cost impact that attracts the most attention. This is, in part, because RTot quantifies an effect that is widely recognized but difficult to measure. [2] But, it is also because RTot expresses an increment of cost with a budget impact that is easy to appreciate. The metric naturally draws notice from stakeholders sensitive to budget changes.
- For impediments and constraints, it is schedule impact that attracts the most attention. This is, in part, because delay in initial value delivery is highly visible—a simple Gantt chart makes gaps abundantly clear. But, it is also because the cost impact of I/C$Tot is not so easy to appreciate. It is visible only as an opportunity cost, and such costs do not seem to carry the same weight as their incremental cousin. [3]
So, RTot and I/C$Tot represent different aspects of noncompliance, both of which should be considered in managing schedule performance.
Finally, the sum of RTot and I/C$Tot can be compared with allowances for late delivery.
- Assuming that such allowances have been included in Contingency and Reserve, there is a quantitative benchmark against which variance can be assessed. When variance trips an alarm for action, the previously described response follows (generically: analysis, planning, remediation). The only difference is that root causes almost certainly will vary between the two sets of tasks.
When uncertainty allowances address both rework and impediments/constraints, [4] RTot and I/C$Tot should be combined before making any assessment against thresholds.
Thus, RTot and I/C$Tot offer new insights into schedule performance. On the other hand, the combination also introduces some limitations. They are spelled out in the next post.
Notes:
[1] It is possible, but improbable, for rework to occur without delay. If a task is finished ahead of time, and it is reworked before the finish date, there is no apparent delay. Such outliers are not captured by the theory.
[2] The schedule impact of rework is not readily visible. Increases in work are automatically reflected as increases in EV by scheduling tools like MS Project. Extensions of finish date do not distinguish between rework and simple overruns. The most obvious indicator of rework is an increase in actual cost, but schedules do not explicitly portray costs. So, the amount and impact of rework is difficult to see through the schedule alone. Walt’s mathematical model offers an innovative way to measure that amount and its associated cost.
[3] A benefit that is not obtained seems more abstract than a cost that is added. As a counter to this attitude, consider an analogy: the absence of someone can be as keenly felt as the presence of someone. Maybe, it’s just an attitude adjustment that brings opportunity costs to the fore.
[4] In practice, it is rare to see rework and impediments/constraints explicitly addressed by Contingency and Reserve. Instead, uncertainty allowances tacitly cover both. To prepare for assessments, it is best to assess whether to treat RTot and I/C$Tot separately or in combination. |
