Concept: The necessary balance between R-tasks and I/C-tasks undermines their use for trade-offs. A deeper concern is the intuition that work done ahead (R-tasks) and work whose start is delayed (I/C-tasks) should be more independent than suggested by ES theory.
This post offers the first step to resolve the concerns.
Practice: As shown in the last post, the “necessary balance” between R-tasks and I/C-tasks conflicts with intuition. In summary:
On one hand, the “necessary balance” implies that impediments/constraints entail rework. But, that conflicts with the intuition that the connection is contingent rather than necessary. Experience seems to support contingency: when we observe rework, we don’t automatically think it’s the result of impediments or constraints.
On the other hand, the “necessary balance” implies that rework entails impediments/constraints. Again, that conflicts with intuition. We sometimes see premature work on one task delaying the start of work on another task. But, we think that, surely, rework doesn’t always have such a consequence.
What underlies both cases is an assumption, namely that the relationship between impediments/constraints and rework is causal. As causal relationships might or might not hold, they are contingent rather than necessary.
Causality exerts a powerful psychological force. Research has shown that “finding causal connections is … an automatic operation” (Kahneman, 2011). It is part of thinking that is fast, instinctive, and unconscious—the default mode for thinking (ibid.). Thus, it is no surprise that we find the conflicting intuitions plausible.
In contrast to fast thinking and its intuitions, there is thinking that is conscious, effortful, and (comparatively) slow. Again, this has been explored thoroughly by researchers (ibid.).So-called “slow thinking” is endemic to formal frameworks, such as science, statistics, and applied mathematics. [1] And, that is where we find resolution of the concerns.
Conflict between intuitions and formal frameworks is a familiar phonomenon. Consider the following common-sense judgments, all of which conflict with science: “heavy objects fall faster than light ones”, “evolution guarantees organisms have the traits they need to survive”, or “ferns grow in forests because they provide ground shade” (Shtulman, A. and Harrington, K. 2016).
Although common, conflicts with intuition are not conclusive. If they were, many formal frameworks would be in doubt. It is precisely this type of framework that Earned Schedule brings into play.
Although intuitive conflict does not invalidate the “necessary balance” between R-tasks and I/C-tasks, it does force clarification of the context for the connection.
How does ES theory assure the equivalence between R-tasks and I/C-tasks? Let’s first consider how it works in practice and then consider a broader justification.
Case Study: Rework Without Impediments/Constraints?
Let’s start with a base case, in which the project is on schedule; there is no rework; and there are no impediments or constraints. Modifying a familiar example to fit these requirements yields Figure 1.
Figure 1
Now, let’s change just one task: assume that Task 5 has all originally planned value earned as of AT. This can be depicted as follows:
Figure 2
The value earned for Task 5 forms a salient well ahead of the other tasks. Isn’t this a case in which there is Rework without counterbalancing Impediments/Constraints?
Not so fast. Recall that the relevant values are EV@AT and PV@ES. The Actual Time has not changed, but what about ES? ES is calculated from EV up to and including AT and PV up to the time at which EV < PV. [2] In Figure 3, the ES time is no longer the same as AT. Instead, the ES time is slightly later than AT due to the additional value earned by Task 5.
To be precise, in Figure 1, ES time = 3.00. In Figure 3, ES time = 3.20. So, according to the theory, ES has moved, and the correct representation is this:
Figure 3
Moving ES to its correct position exposes tasks that are impeded or constrained, specifically Tasks 2 and 6, where the PV@ES is unfulfilled. The interworking of ES and P-Factor ensures that the value in R-tasks equals the value in I/C-tasks and vice versa.
That’s how the theory works to maintain the balance, but the explanation might appear wanting. Is the relationship purely formal, i.e., merely the conclusion to an abstract, logical inference? Is it without any causal, psychological, or practical significance?
The answer lies in a broader view of the ES framework.
Notes:
[1] The first judgment demonstrates the robustness of such intuitions. Although repeatedly falsified by experiments (including one performed by astronaut David Scott on the moon), the intuition continues to be tested. In fact, a recent test “…found no discrepancy in the acceleration of two small test masses to about one part in 100 trillion (1014)” (Galileo’s Free Fall Tested Again). Amazingly, testing will not stop there—a further test is planned to prove it holds to 1 in a quadrillion! That’s a testimony to the power of the conflicting intuition.
[2] That time is called the “ES Time” or simply “ES” for short. The terminology can get a bit confusing, as the overall theory is referred to as “Earned Schedule” or, again, “ES” for short. In the text, I use “ES time” rather than simply “ES”, with one exception. When referring to planned value as of a specific time, I use the abbreviation PV@ES. That’s short for PV@ES time. (NB In the diagrams, I use “ES” for “ES time”.)
References:
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).
Lipke, W. (2008b). Earned Schedule - Schedule Analysis from EVM Measures. Project Landscape, July 2008. and in his
book Earned Schedule, p 14).
Lipke, W. (2008a). Schedule Adherence: A Useful Measure for Project Management. CrossTalk, April 2008.
Shtulman A, Harrington K (2015) Tensions between Science and Intuition across the Lifespan. Topics in Cognitive Science 8:118–137. https://doi.org/10.1111/tops.12174.
|
