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The PERT Formula
The main reason a project manager will want to use the PERT Formula is to have an estimate for cost or duration that is accurate. When project managers - especially inexperienced ones - estimate duration, sometimes they choose an amount of time that is too short or too long. The same scenario also happens with cost.
At times, if a formula isn't used for determining the estimated cost, a project manager may budget too little monies for the project. However, initial estimations aren't the only times when the PERT Formula is useful. It is also useful with project crashing and fast-tracking projects.
To learn how to manually calculate using the PERT Formula, check out Linda Richter's article, Project 2007: Estimating Task Duration Using the PERT Formula.
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When you crash a project, you attempt to speed up the time it takes to complete a project task by allocating more money to that task. For specific information concerning how to crash a project, see Diana Hardin's article, A Quick Guide ot Crashing a Project Schedule.
In order to know how long a given task within the project would take, an estimate must be made. Using the PERT Formula is one way to estimate how long the task will take under normal circumstances, By having this estimate, and the cost estimate for this period of time, knowing which method to use to crash the project becomes easier.
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Fast-Tracking Projects and the PERT Formula
Crashing project schedules is not the only method to speed up a project schedule that is lagging behind. Another option for speeding up the project schedule is to fast-track the schedule.
Fast-tracking requires that rather than work on tasks in a sequence the tasks are worked on either concurrently or semi-parallel to one another. For more information on fast-tracking a schedule, see my article, Project 2007: Fast-Tracking a Project Schedule.
Knowing the PERT Formula estimates can facilitate fast-tracking by helping you to determine which of your tasks are the most likely to successfully fast-track.
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The PERT Formula and Risk
Another time when a PERT Formula calculation might be used is when a project task contains some risk with it. In fact, some project managers only use the PERT Formula in a case where risk assessment determined high risk in a task. This gives the project manager flexibility in scheduling risky tasks, and it protects against some of the surprise of actualized risk.
For more information on risk management, see my article Determining the Level of Risk in a Project.
When Should You Use the PERT Formula?
This series of articles introduces readers to the PERT Formula and discusses applications of PERT in project management.