The Program Evaluation and Review Technique (PERT) is a project management tool used to plan, schedule, and control complex projects. Unlike traditional project management techniques that use deterministic time estimates for tasks, PERT employs probabilistic time estimates to account for uncertainty. This is especially useful in projects where task durations are uncertain and can vary.
Origins of PERT
PERT was developed in the 1950s by the U.S. Navy in association with the Booz Allen Hamilton consulting firm for the Polaris submarine project. Its purpose was to enhance the planning and control of large-scale, complex projects with significant uncertainties in task durations.
Key Concepts and Definitions
Probabilistic Time Estimation: PERT uses three different time estimates to calculate an expected duration for each task:
- Optimistic Time (O): The shortest time in which the task can be completed.
- Pessimistic Time (P): The longest time the task might take.
- Most Likely Time (M): The best estimate of the time required for the task, assuming everything proceeds as normal.
Expected Time (TE): This is calculated using the formula:
PERT Chart
A PERT Chart is a visual representation of a project’s timeline and task dependencies. It is a type of network diagram that displays the sequence of activities and the pertinent time frames for their execution.
Applications of PERT
PERT is highly applicable in:
- Research and development projects.
- Military and aerospace projects.
- Large-scale engineering projects.
- Industries with high levels of uncertainty and complexity.
Advantages of PERT
- Handling Uncertainty: Provides a systematic way to manage uncertainty in project timelines.
- Improved Planning and Scheduling: Offers a clear visualization of the project schedule and task dependencies.
- Better Resource Allocation: By identifying critical and non-critical tasks, it aids in efficient resource distribution.
Limitations of PERT
- Complexity: Can become unwieldy for projects with a large number of tasks.
- Subjectivity in Estimates: Relies on the accuracy of the time estimates, which can be subjective.
Example
Consider a project to develop a new software. The task estimates might be:
- Optimistic Time (O): 6 months
- Most Likely Time (M): 9 months
- Pessimistic Time (P): 18 months
Using the PERT formula:
Historical Context
The development of PERT represented a significant advancement in project management during the mid-20th century. It was initially used for the Polaris missile program, which was successful in meeting its stringent timelines and performance goals.
FAQs about PERT
Q: How does PERT differ from CPM (Critical Path Method)? A: While both PERT and CPM are project management tools, PERT uses probabilistic time estimates suitable for projects with high uncertainty, whereas CPM typically uses deterministic time estimates for task durations.
Q: Can PERT be used for small projects? A: Although PERT is particularly beneficial for large and complex projects, it can be applied to smaller projects where uncertainty in task durations is a concern.
References
- Project Management Institute (PMI). “A Guide to the Project Management Body of Knowledge (PMBOK® Guide).”
- U.S. Department of Defense. “Polaris System Development.”
Summary
The Program Evaluation and Review Technique (PERT) plays a pivotal role in managing projects with uncertain durations of tasks. By employing probabilistic time estimates, PERT provides a structured approach to planning, scheduling, and controlling complex projects, ensuring efficient use of resources and better timeline management. While it offers numerous advantages, it also comes with limitations that need to be addressed with careful planning and expertise.
