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 and the future impact of that efficiency level.
A less familiar metric, schedule adherence, measures how well or poorly the planned sequence of deliverables is being followed. It can also be used to detect the specific tasks that are degrading schedule performance.
Let’s start with the difference between schedule efficiency and schedule adherence.
Figure 1
Practice: The difference is like the difference between the fuel efficiency of a car and its wheel alignment.
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 capability of your vehicle.
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.
So, 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.
Consider the Schedule Performance Index for time (SPIt). It 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.
Or, consider the Estimate at Completion for time (EACt). It 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.
That’s where schedule adherence fits. For adherence, the sequence of delivery matters very much.
Like wheel alignment, schedule adherence is either on plan or off plan. If completions exactly align with the plan, the schedule adherence is a perfect 1.0. If there is no alignment with the plan, schedule adherence is 0.0. Generally, the value lies between the two extremes.
Here’s an example.
Figure 2
In Figure 2, some deliverables are impeded and are therefore considered to be late, e.g., 2, 4, and 6. Other deliverables are completed before their predecessors are done, e.g., 7 and 8. As they proceed with incomplete knowledge, they will likely require rework.
The value missing from late deliverables is offset by the value gained from early deliverables. ES is the balance point between the volume impeded and that likely to require rework.
By comparing the value earned as of the Actual Time to the value planned as of the ES time, we can identify where the order of delivery is not being followed. That gives insight not only into how much deviation there is from plan but also what tasks contribute to the deviation.
When does adherence matter?
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 requirement 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.
Schedule adherence, however, 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.
References
Lipke, W. (2020). Chapter 12. Earned Schedule Plus. Gatekeeper Press.
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. |
