Concept: ES theory maintains that there is a balance between the value of R-tasks and of I/C-tasks. The mechanism that maintains the balance might appear to be purely formal, an engine of abstract, logical inference. If so, that seems to drain the “necessary balance” of impact.
Is the “necessary balance” truly without any causal, psychological, or practical significance? The answer lies in a broader view of the ES framework.
Practice: What bridges the gap between the formal mechanism and its impact is a footing for the math.
As Glen Alleman says, “Without principles, practices and processes have no home on which they can be validated” (Alleman, 2020, January 12; see also, Alleman, 2020, March 05).
The “home” for ES is a deceptively simple principle. It is one not often called out explicitly in the ES literature. In fact, its most telling expression appears only as a comment on a diagram: “The idea is to determine the time at which the EV accrued should have occurred” (Lipke 2008a). [1]
That is, the idea behind Earned Schedule (as a framework) is to determine the time at which the value currently earned should have been earned. It follows that the ES time is the balance point between EV@AT and PV@ES. How so? First, let’s deconstruct the principle to clarify what it expresses. Then, we’ll look at its justification.
In the principle, “the EV accrued” is the total value that is earned, but as of what point? Given that we are assessing current schedule performance, it makes sense to capture all and only the EV at the Actual Time. That represents the achievement during the elapsed time, i.e., EV@AT.
Next, the “value that should have occurred” refers to the value planned to be earned, but, again, as of what point? Given that we are assessing how much of the plan has been fulfilled, it makes sense to capture the PV at the limit of fulfillment. Planned value is being fulfilled as long as EV >= PV. Fulfillment up to that point represents the achievement during the earned time, i.e., PV@ES.
Finally, the principle links the two terms as equivalents, i.e., EV@AT=PV@ES. So, the ES time is the point at which this occurs and is, therefore, the balance point between EV@AT and PV@ES (i.e., EV@AT – PV@ES = 0). [2]
Now, let’s look at justifications for the principle.
Note first that it is a normative principle, as signaled by the use of the word, “should”. Normative principles are usually contrasted with empirical ones. Empirical principles are descriptive; norms are prescriptive (O’Neill 2018).
Normative principles are often difficult to justify. Sometimes, justification is an appeal to authority. Other times, the appeal is to public consensus. Neither of those justifications seems to be compelling here.
A third way to justify a normative principle is teleological: to connect it with an end or objective that is desired. As O’Neill puts it:
Normative reasoning does not aim to be true of the way things actually are [that’s for empirical reasoning], but to specify standards or principles for action and practices, which if adopted may also be formative for the states of affairs to which activity leads. (O’Neill 2018, in “Normative reasoning in scientific practice”.)
Presumably, on time delivery is a desired “state of affairs” for projects. One way to ensure it is to accrue Earned Value in the planned volume and in the planned sequence, i.e., in the amount and at the time it was scheduled to have occurred. The practice of measuring conformance with the plan and of adjusting the project in the light of such measurements is formative for achieving on-time delivery—therein lies the justification for the principle.
Therein also lies the significance of the balance between EV@AT and PV@ES and the consequent balance between the value of R-tasks and I/C-tasks. (See Appendix Bfor a proof that the balance of EV@AT and PV@ES entails the balance between R-tasks and I/C-tasks.)
If we take the principle seriously, we must adhere to the schedule or pay the price. In this context, the “price” for deviations is always two-fold: value earned before and value earned after it was planned. The former cases are R-tasks and the latter are I/C-tasks.
The implication is clear. If a gap opens between AT and ES time, there must be both Impediments/Constraints and candidates for Rework. By managing both, the project will be brought back on track.
Thus, the ES principle ensures the practical significance of the math, and in doing so, it takes account of more drivers of schedule performance than does causal intuition.
Appendix A:
ES is calculated from EV up to and including AT and PV up to the time at which EV < PV. In the figure below, the ES time is slightly later than AT due to the value earned by Task 5.
To be precise, in the figure, ES time = 3.20. With ES in this position, impeded/constrained tasks are exposed, 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.
Appendix B:
Notes:
[1] See also Lipke (2008b) and Lipke (2011).
[2] Note that the ES time is the balance point between the value planned and earned. It is not necessarily the balance point between the number of R-tasks and I/C-tasks. This limitation is clearest when the project is ahead of schedule. See Appendix A for an example. In it, both R-tasks and I/C-tasks occur between AT and ES.
References:
Alleman, G. (2020, March 05). All Project Success Starts with Applying Principles. Retrieved from https://herdingcats.typepad.com/my_weblog/2020/03/all-project-success-starts-with-applying-principles.html.
Alleman, G. (2020, January 12). Quote of the Day. Retrieved from https://herdingcats.typepad.com/my_weblog/2020/01/quote-of-the-day-6.html.
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 p 14).
Lipke, W. (2008a). Schedule Adherence: A Useful Measure for Project Management. CrossTalk, April 2008.
O'Neill, O. (2018). Scientific inquiry and normative reasoning. In From Principles to Practice: Normativity and Judgement in Ethics and Politics. (pp. 40-52). Cambridge: Cambridge University Press. doi:10.1017/9781316286708.004. |
