Concept: Schedule Adherence is like the wheel-alignment of a car: there can be perfect alignment, but things often get out-of-balance. When that happens, we can measure the amount of deviation from true.
For Schedule Adherence, the measurement is conceptually simple but practically difficult.
Conceptually, the measurement is the per centage of value earned exactly as planned.
Figure 1
Practice: Practically, measuring Schedule Adherence is made difficult by the level of detail required. Each atomic [1] task in the schedule must be examined. That can be challenging because schedules can contain hundreds, if not thousands, of tasks.
For each task, the following questions need to be answered: does the task contribute the value it is planned to contribute when it is planned to contribute it? If not, is it incomplete, or alternatively, does it deliver value prematurely?
The answers depend on the task’s PV as of the ES Time and EV as of the Actual Time. If the task’s EV@AT equals its PV@ES, the task is on schedule. If a task’s EV@AT is less than its PV@ES, the task has not earned value at the planned pace. It is running behind schedule and is impeded or constrained in some way. If a task’s EV@AT is greater than its PV@ES, it is being done prematurely and runs the risk of rework.
As illustrated by Figure 2, Tasks 1 and 3 are on schedule. Tasks 2, 4, and 6 are running late. Tasks 5, 7, and 8 are early.
Figure 2
The difference between each task’s PV@ES and EV@AT indicates how the task is performing.
From the differences across all tasks, we can build a measurement of Schedule Adherence—the P-Factor. It is the percentage of actual value delivery that is exactly aligned with the planned sequence of value delivery.
To calculate the percentage, divide the amount of aligned value by the amount of planned value.
The tricky part is how to identify all and only the value exactly aligned with the schedule. Inspection of a network diagram as in Figure 2 does not scale. Fortunately, Walt Lipke has identified a numeric approach that highlights value earned out of sequence. It’s useful to represent the approach in tabular form.
Figure 3
In Figure 3, the table identifies each atomic task and displays the task’s total Planned Value. Then, it shows the task’s PV at the ES Time, EV at the Actual Time, and the difference between the two values. Finally, it shows the amount of EV that is aligned with the schedule, including the value from incomplete tasks but excluding value from premature tasks.
For each difference, the sign (or its absence) indicates whether or not the EV@AT is aligned: if the sign is positive, the EV@AT is not aligned; otherwise, the EV@AT is aligned.
To illustrate, here is an example. It starts with the raw data that’s behind the curves in Figure 2.
Figure 4
Keeping in mind that the ES Time is exactly the end of Period 3 and the Actual Time is exactly the end of Period 4, the totals for each task are listed in Figure 5 under the headings PV, PV@ES, and EV@AT. The totals are followed by the difference between the EV at the Actual Time and the PV at the ES Time. The final column indicates how much EV is aligned with the scheduled delivery of value as of the ES Time.
Tasks 1 and 3 have EV@AT = PV@ES and a difference of 0. Such tasks are on schedule, and their value is included in the amount that adheres to the schedule.
Tasks 2, 4, and 6 have EV@AT < PV@ES and a negative difference. Such tasks are impeded or constrained and have fallen behind schedule. That has two effects. First, their incomplete value contributes to the ES Time falling earlier than the Actual Time, i.e., a gap opens between the two times. Second, although incomplete, the portion of the task that has been done as of the Actual Time is still in sequence. That portion is added to the amount adhering to the schedule.
Finally, Tasks 5, 7, and 8 have EV@AT > PV@ES and a positive difference. Such tasks are being done prematurely. The value delivered from those tasks falls in the gap between the ES Time and the Actual Time and is excluded from the total that adheres to the schedule. In the P-Factor calculation, these amounts are subtracted from the EV at the Actual Time.
As shown in Figure 5, the total amount of value planned as of the ES Time is 40. Most of that value has been earned in accordance with the schedule, even if some of it is incomplete.
There is, however, value that has been earned that is not aligned with the schedule. It is identified by positive differences between EV@AT and PV@ES. In the example, the total is 7, and it is excluded from the aligned value.
Thus, 33 of the 40 units planned to be done as of the ES Time were delivered exactly as sequenced, and that makes the P-Factor equal 33/40 or 0.825.
The calculation can be expressed succinctly by the following formula:
EV denotes the value earned, PV denotes the value planned, and, most important, the subscripts “i” and “j” denote the target tasks.
The target tasks for the PV is the set of tasks scheduled (S) for delivery (in full or in part) as of the ES Time.The target tasks for EV is a subset (“i”) of the “j” tasks, specifically, just the “j” tasks that have delivered value aligned (A) with the PVj as of the ES Time.
So, the formula reads as: the P-Factor equals the total value actually earned in alignment with the schedule divided by the total value that should have been earned as scheduled. In both cases, the value is as of the ES Time.
Next month: P-Factor Limits and Limitations
Note:
[1] An “atomic” task represents a stand-alone deliverable. It does not cover the detailed steps that are required to create a deliverable. Nor does it represent a collection of deliverables such as a User Story. The assumption here is that estimates and schedules are developed and maintained at the atomic level, not at a summary level.
References:
Lipke, W. (2013). Schedule Adherence …a useful measure for project management. PM World Journal, Vol II, Issue VI.
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. (2009b). Earned Schedule. Lulu
Lipke, W. (2009a). Schedule Adherence …a useful measure for project management. The Measurable News, Issue 3.
Lipke, W. (2008). Schedule Adherence: AUseful Measure for Project Management. CrossTalk, April. |
