No Critical Path! What Is a Project Manager to Do?
February 10th, 2004 by HalOur common sense understanding of projects has us believe there is a critical path that must be followed if we are to be successful on our project. Many contracts require that an 'accurate representation of project priorities' be represented as a critical path. Here's what I said in my state of the art assessment:
- There is no critical path. Of course I'm not saying that one can't calculate a critical path. Of course you can calculate it. I'm saying that it is not a thing, just a characterization.
Like anything, a CPM schedule is only as useful as the data that is available for doing the calculations. CPM schedules use task and duration data for the calculation of the critical path. The problem is the data is not fact. The only project facts we have on task effort and durations is available after the tasks are completed. At that point critical path calculations have limited value.
The dirty secret of construction projects is the critical path schedule is not critical.
Schedules are constructed using estimates of task durations and task dependencies. Goldratt showed us the effects of dependence and variation on the predictability or reliability throughout a project. At best we have reasonable estimates. But they are estimates. Rarely do people take the time to produce estimated ranges of effort and duration. Consequently, our schedules fail to represent the stochastic (probabilistic) nature of the project. Yet we treat our schedules as if they are deterministic. This is the fundamental flaw in our use of the critical path method.
The dirty secret of construction projects is the critical path schedule is not critical. Construction superintendents and project managers have their own set of priorities that dictate what gets done first. For more on my views read: CPM: Fool Me Once, Fool Me Twice.
What is the project manager to do? Paraphrasing David Schmaltz, project managers already know what to do, and many are already doing it. How about the rest of you?
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February 11th, 2004 at 2:49 pm
It’s what one might call a model of current expectations. The model/map is not the thing/territory.
January 23rd, 2007 at 11:38 pm
I know this is an old post but I’d like to leave a comment anyway. It’s so true that estimates are treated as if they are deterministic and set in stone. It’s almost like people are surprised when tasks go over. There may be a false sense of security coming from the Parkinson’s law, which makes it appear that for the most part tasks aren’t finishing early, so there’s some phantom characteristic that looks like some certainty.
When I learned critical path methods in school, they treated the estimates as if they were deterministic, and it all looked so nice and clean when calculating the critical path, etc.
Josh Nankivel
http://www.PMStudent.com