So What Do Dependence and Variability Have to Do with Projects?
August 29th, 2002 by Hal
In the usual practices of project management establishing precendence relationships is a key step in creating a network plan for the project. Along with that the planner often establishes early and late start dates and a finish date. But these dates have nothing to do with what will be done when the time comes for the task. Why? One reason is due to the variation of task completion throughout the project. We can count on each task taking a different effort and duration than was originally planned. Let's consider an example:
The engineering specification expected to take 20 hours and due on the 15th of the month actually took 30 hours and was completed on the 20th. Further, the task was planned for one person, but that person needed others' help. To the extent that other work couldn't begin 'til the spec was ready (a usual case for a spec), the project accumulates delay. Further, there is less engineering hours available than were originally planned due to the variance in effort of the enginneer and the help provided by others. While it is true that some tasks take less effort than estimated, our project experience tells us that we rarely benefit from early completions. So we have a project that will require more hours and more duration than originally planned.
What can be done? First, one must identify the situations that are likely to vary from the planning estimates. Then, buffer other tasks from that variability and work to reduce the variability. How? For recurring tasks one can study the flow of work, reduce the waste, minimize ambiguity, and appropriately staff the task with necessary skills. Is this enough? No, because we have variablility popping up all over. The solution then must be systemic and organizational. (more to come)
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