PERT is a project management tool that helps to plan, organize, estimate, coordinate and coordinate tasks within a project. PERT stands for Program Evaluation Review Technique. This methodology was developed by the U.S Navy in the 1950s to manage its Polaris submarine missile program.
There are two versions.
PERT Chart – Used for project scheduling
Three point estimation is also known as PERT estimation.
A PERT chart is a visual representation of a project. It is similar to a network chart. It consists of numbered nodes in the form of rectangles or circles, which represent events or milestones in the project. These nodes are linked by labelled vectors, or directional lines, which represent tasks in the project.
The direction of the arrows along the lines defines the sequence of tasks. The following diagram shows an example of a PERT Chart.
It is important to complete the tasks between nodes 1, 2, 4, 8 and 9 in a specific order. These are known as dependent or serial tasks.
The tasks between nodes 1, 2, and 3, are not dependent on one another and can be done simultaneously. These tasks are known as concurrent or parallel tasks.
Tasks that must be completed in a specific order but don’t require resources nor completion time are called event dependency. These are represented as dotted lines with arrows, and are called dummy tasks. The dashed Arrow linking nodes 6 to 8 is an example.
The numbers on either side of the vectors indicate how much time was allotted for the task.
Although it is similar to Gantt charts, Pert chart can sometimes be preferred over Gantt charts. It is clear and easy to see task dependencies. PERT chart has a disadvantage. It’s more difficult to understand, especially when you are dealing with complex projects that have many dependencies. It all depends on how comfortable the Project Manager is with the tool.
This technique is also known as Three Point Estimation. This idea was inspired by the program evaluation and review method (PERT). PERT uses three estimates in order to determine an approximate duration for an activity.
Most likely (tM). This estimate is based upon the duration of the activity, the resources likely to have been assigned, their productivity, realistic expectations about availability for the activity and dependencies on other participants.
Optimistic (tO). Based on the best-case scenario, the duration of the activity is calculated.
Pessimistic (tP). Based on the worst-case scenario, the duration of the activity.
A formula can be used to calculate the expected duration based on the assumed distributions of values within the ranges of the three estimates. Triangular and beta distributions are two common formulas. These formulae are:
Triangular Distribution tE = (tO+ tM+ tP)
Beta Distribution (from the PERT traditional technique). tE = (tO+ 4tM + 6tP)
Three points with an assumed distribution are used to estimate the duration. They provide an estimated duration and help clarify the uncertainty surrounding the expected duration.