Concept: To make sound schedule decisions, we need to measure progress on the baseline schedule. Without such measures, decisions become haphazard. With the metrics, you know where the project stands and is likely to go. Metrics can even point to the source of schedule problems. Such information grounds decisions on what to do next.
ES offers several metrics for measuring schedule progress. The most familiar ones, SPIt and EACt, express the efficiency with which the plan is being executed. [1] A less familiar metric, Schedule Adherence, measures how well or poorly the planned sequence of deliverables is being followed. [2] It can also be used to detect tasks that are hurting schedule performance.
The next few posts focus on Schedule Adherence.
Figure 1
Practice: Figure 1 will be used repeatedly in the following posts and deserves an introduction. [3]
The bottom part of the chart gives an overall view of how value is planned and earned on the project. The curves represent the cumulative Planned Value (PV) and Earned Value (EV) of the deliverables over a set of time periods (vertical lines). The Earned Schedule (ES) is the time when the value that has been earned should have been earned. The end of the project marks the total budget (BAC) and planned duration (PD).
The top part of the chart shows how specific deliverables can fail to follow the plan. The boxes represent project deliverables (aka, Outputs or O/P) with planned duration. Shading covers the portion of the deliverables that has been completed as of the Actual Time (AT). The unshaded areas to the left of the ES line mean that delivery has been impeded in some way. The shaded areas to the right of the ES line mean that deliverables have been completed before their predecessors and are likely to require rework.
More on the chart later, but now, let’s look at the difference between Schedule Efficiency and Schedule Adherence. The distinction is an important one, and it needs to be spelled out.
An analogy will help.
Figure 2
The fuel efficiency of a car measures the miles you can travel on a certain amount of gas. From the mileage, you know if you are where you should be given the fuel that has been burned. Your actual mileage on a trip can be above, below, or at the rated capacity of your vehicle.
Figure 3
Extending the analogy, for your car to run straight, its wheels must be properly aligned. The wheels are either in alignment or they are not, and although they can be wildly out of line, they cannot be better-than-aligned.
Like fuel efficiency, Schedule Efficiency tells you whether the volume of delivery meets the plan and whether that puts you where you should be on the timeline. The SPIt reflects how much of the value currently earned matches what should have been earned. If the SPIt is at or above 1.0, the current value is at or above the planned amount. Otherwise, there’s a shortfall in the volume of delivery.
The EACt, in turn, expresses the impact of the volume delivered thus far. If the volume is at or above plan, the estimated duration is at or less than the planned duration. Otherwise, the estimated duration is beyond the plan, and the project is running late.
What’s missing from these measures is information about how the value is being delivered. That is, SPIt and EACt do not reflect the sequence in which deliverables are being completed.
It might be that some deliverables are impeded and are therefore late, such as 2, 4, and 6 in Figure 1. Or, it might be that some deliverables are being completed before their predecessors are done, such as 7 and 8. As they are proceeding with incomplete information, they are likely to require rework.
At the same time, the value missing from late deliverables can be offset by the value gained from early deliverables. Figure 4 depicts what this would look like. The shortfall in 2 is mostly balanced by the early delivery in 7, and the shortfalls in 4 and 6 are largely balanced by the early delivery in 8. A small difference remains, however, between the total amount of value planned by AT and the total amount earned by AT.
In such a case, the ES time moves closer to the Actual Time but does not match it. The SPIt would be slightly below 1.0 and the EACt slightly beyond the PD. Such small discrepancies might not trigger warnings. That’s where Schedule Adherence will help.
Figure 4
For Schedule Adherence, it matters very much which deliverables are completed. If the completions exactly align with the plan, the Schedule Adherence is a perfect 1.0. If there is no alignment with the plan, the Schedule Adherence is 0.0. At most times, the value lies between the two extremes.
Schedule Adherence detects cases in which the volume of delivery is at or near the expected level, but the order of delivery is not being followed.
A real-life case occurred on a recent project. The Project Manager wanted the team to develop a habit of delivering on time. She observed that progress on requirements definition was beginning to slow due to the number of unresolved issues. To break the logjam, she allowed “conditional sign off”. That meant a requirements document could be declared as finished even though it still had unresolved issues.
The project team quickly took advantage of the change. They declared requirements finished for the increment that was underway and made an early start on its design. The SPIt and EACt for the project looked good.
Fortunately, the Schedule Adherence metric, sensitive to out-of-sequence activity, signaled that there was a problem. Root cause analysis by the Project Management Office revealed what was behind the anomaly. The likelihood of rework was discussed with the PM, and she modified the approach to account for that probability.
Measures of efficiency and adherence are often congruent. When they are not, the divergence is informative. It can show that the volume of delivery is masking work being done out-of-sequence. That’s why it’s good practice to have both metrics available when managing the schedule.
Glossary:
EACt = Estimate at Completion for time; estimated duration based on past performance
ES = Earned Schedule; both the generic term for the approach and a specific metric, namely, the amount to time earned on the project
PM = Project Manager--the person with overall responsibility for the delivery of project objectives. In an Agile project, the responsibility and associated tasks are often shared among team members
PMO = Project Management Office (aka, Program Management Office)--the organizational entity responsible for the centralized and co-ordinated management of projects (or large program) under its domain; responsibilities range from PM support to direct responsibility for projects
SPIt = Schedule Performance Index for time; the amount of ES divided by the Actual Time; a measure of schedule performance efficiency
Notes:
[1] For posts on SPIt, click here. For posts on EACt, click here.
[2] Walt Lipke has addressed Schedule Adherence in several articles, some of which are reprints. See References for a complete list. My posts are sourced primarily from Lipke (2009a) and Lipke (2011a).
[3] The chart in this form appears frequently in Walt's articles on Schedule Adherence. Later in this post, I modify it slightly to tell a different story from the one told here.
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: A Useful Measure for Project Management. CrossTalk, April. |
