CPM: Fool Me Again
October 2nd, 2002 by HalArticle Series - CPM: Fool Me Once, Fool Me Twice
Task durations vary.
Experienced project managers will tell you the critical path moves on a project. Why? Tasks don't start and finish as represented in the project schedule. This would be fine if all the performers for critical path tasks were always available to perform on the project, but this is not the case. In most organizations people are working on more than one project at a time or project work is in addition to their normal work responsibilities. This creates the situation where they must manage priorities: "Do I spend my time on this or on that?"
Our only avenue is to manage the project to minimize the variability.
We don't know all of what must be done. Oftentimes ad hoc work (those tasks that seem to arise in the course of doing the other work) encompasses as much time as the planned work of the project. To the extent that this ad hoc work requires the same resources as the work on the plan we see projects get behind. Performing this work often shifts the critical path.
Task durations therefore are probabilistic. They will range from times that are as short as the actual time applied performing the task to as long as multiples of the task times depending on how much waiting time and distraction time is incurred. Projects by their nature make it difficult to gauge those probability distributions because each project is unique. Our only avenue is to manage the project to minimize the variability.
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October 7th, 2002 at 7:45 pm
The SCRUM Agile Development Process specifically avoids GANT charts because the critical path changes in real time from day to day for many reasons, including the ones commented on. It uses daily meetings where the entire team understands the global scope to fine tune the critical path in real time. The neural networks in the brains of the developments are faster and smarter than a project manager with a GANT chart.