Program Evaluation and Review Technique (PERT)
The Program Evaluation and Review Technique (PERT) is a statistical tool used in project management, which was designed to analyze and represent the tasks involved in completing a given project. It was first developed in the late 1950s by the U.S. Navy for the Polaris missile program to help manage complex and large projects.
PERT involves identifying the time it will take to complete the activities in a project, and it shows the sequence of activities. The activities are represented in a PERT chart, where nodes represent tasks and arrows show dependencies between tasks.
Key features of PERT include:
- Multiple time estimates: Unlike other techniques, PERT uses three time estimates for each activity: optimistic time (if everything goes perfectly), pessimistic time (if everything goes wrong), and most likely time (under normal conditions). This allows for the uncertainty inherent in project activities.
- Critical Path: PERT helps identify the “critical path,” which is the sequence of tasks that must be completed on time for the entire project to be completed on time. Any delay in the critical path activities delays the entire project.
- Slack Time: PERT also helps in identifying “slack” or “float” time, which is the total time that you can delay a task without delaying the project. More slack time means that project scheduling is more flexible.
Here’s how the PERT formula works:
Expected Time = (Optimistic Time + 4 x Most Likely Time + Pessimistic Time) / 6
The PERT method aids in the coordination and scheduling of tasks to reduce waste and enhance efficiency and productivity. While it is quite useful, it’s important to note that PERT’s effectiveness depends on the accuracy of the estimated times for activities. It is also more suited to larger and complex projects where time scheduling is very crucial.
Example of Program Evaluation and Review Technique (PERT)
Let’s take an example of a very simplified project which involves three activities:
- Activity A: This is the first task and it doesn’t depend on any other task. The optimistic time to complete the task is 3 days, the most likely time is 4 days, and the pessimistic time is 5 days.
- Activity B: This task follows Activity A and can’t start until A is completed. Its optimistic time is 2 days, most likely time is 2.5 days, and pessimistic time is 3 days.
- Activity C: This task can start independently of A and B. Its optimistic time is 5 days, most likely time is 6 days, and the pessimistic time is 8 days.
First, let’s calculate the expected time for each task using the PERT formula:
- Expected Time for A = (3 + 4*4 + 5) / 6 = 4 days
- Expected Time for B = (2 + 4*2.5 + 3) / 6 = 2.5 days
- Expected Time for C = (5 + 4*6 + 8) / 6 = 6 days
So, the sequence of activities A -> B takes 4 + 2.5 = 6.5 days, and activity C takes 6 days.
In this case, the PERT chart would reveal that A -> B is the critical path because it takes the longest time. Any delays in either A or B would delay the entire project. On the other hand, C has a slack time of 0.5 days, meaning it could be delayed by half a day without affecting the overall project timeline.
Remember, this is a very simplified example. Real-world projects would typically involve many more activities, and the dependencies between them might be more complex.