We received a comment asking “is it possible to “roll up” or summarize physical % complete values at the Work Breakdowns Structure (WBS) element level?” Let’s explore this question.
Primavera P6 Professional has three different percent complete types for measuring the progress of activities: duration, units, and physical. The ‘duration % complete’ type is the simplest, as it requires the least input. The ‘duration % complete’ type assumes that the percentage of work achieved relates directly to the remaining duration.
The ‘units % complete’ is preferable for activities that have multiple resource assignments and non-uniform burn rates among these resources. The ‘physical % complete’ type is considered the most accurate, as the percent complete is based on the amount of work physically achieved on the activity, and is separate too, and entered independently of the remaining duration. See Figure 1 below for Primavera P6 Physical % Complete example:
‘Physical % complete’ type is popular in the construction industry where work achieved is easy to measure. ‘Physical % complete’ has one drawback though; it does not “roll up” or summarize values at the WBS level.
This article explains why the ‘physical % complete’ type does not summarize at the WBS level.
As alluded to previously, one attribute of the ‘physical % complete’ type is that it requires more data input. In addition to the % complete of work physically achieved, you also have to provide either the remaining duration or an expected finish date. This negative, however, is outweighed by its more accurate description of work achieved and remaining. (Note that the ‘units % complete’ type also requires more data input.) As mentioned, the ‘physical % complete’ type has an apparent deficiency: the % complete does not “roll up” or summarize at the WBS element level. So what’s up with that?
In our demonstration schedule, Figure 2, we see that the mobilize activity is assigned the ‘physical % complete’ type; it is also 100% complete.
However, notice that the mobilization WBS element does not have a ‘physical % complete’ value. You may further note that the ‘physical % complete’ value does not summarize at the project level. We do have values for ‘duration % complete’ and ‘units % complete’ at the WBS element and project level. The question, again, to be asked “is it possible to “roll up” or summarize physical % complete values at the WBS element level?”
The answer, unfortunately, is no. Why? Or why not? The reason is that the ‘physical % complete’ value is a manually entered value, and is describing an external factor; something that P6 has no basis upon which to perform summarization. The ‘physical % complete’ value is separate from the remaining duration or remaining (labor) units value. The amount of work physically achieved does not directly relate to the remaining duration or units.
To put it another way, the ‘physical % complete’ value is not a duration or (labor) units value; it is a value based on something outside of Primavera P6, like how many pages of a document were written or how many cubic feet of concrete got poured. Elapsed time or units expended is not a measure of progress; the reality of the physical situation is the measure of progress. The values of progress among ‘physical % complete’ activities are dissimilar and cannot be summed.
The ‘duration % complete’ type, however, can provide a sum because it is a duration value, and the remaining duration of each task is directly related to the elapsed time. Progress is measured by elapsed time, which is inherent in the scheduling software program. The elapsed time of individual activities sums and is comparable to the whole time of all activities below a WBS element.
Although the ‘units % complete’ type models, possibly, several resources all with differing burn rates, it can sum because it is units based, such as labor units. And the units % complete relates directly to remaining (labor) units. Although the remaining duration is manually input (much like ‘physical % complete), it is possible to sum the actual units of all resources on all tasks below a WBS element. This is divisible by the whole of all actual and remaining units of all resources on all tasks below a WBS element.
Also, a resource/cost loaded schedule that has been correctly baselined does provide another good percent complete value called Performance % Complete. This has an underlying earned value based metric to drive it, and therefore will provide a fairly good evaluation of summary % complete values at the higher levels for projects that are heavily weighted with physical % complete progress tracking. So there’s one more reason to use resource loaded schedules with good baseline and progress tracking methods wherever possible.
The ‘physical % complete’ type is preferable for measuring progress because it provides a description of the actual work achieved on a task. It does, however, require more manual input of information. But the percentage complete does not “roll up” and summarize at the WBS level for this percent complete type.
You’ll notice this same shortcoming in other tools such as Microsoft Project. It’s not an issue with the software, rather it’s just the nature of physical % complete tracking generally. The ‘units % complete’ or ‘duration % complete’ types may, therefore, be more helpful for gaging the progress of a schedule that has numerous deep layers of WBS element bands. And also keep in mind the use of Performance % Complete, particularly at higher levels and project summary reporting as these are driven by whatever mix of physical and other percent complete types you are using.