What Is a Program Evaluation Review Technique (PERT) Chart?

A program evaluation review technique (PERT) chart is a graphical representation of a project's timeline that displays all of the individual tasks necessary to complete the project. Put simply, a PERT chart is a project management tool that allows users to map out a project's timeline and itemize individual tasks. This means that the PERT chart allows users to communicate project instructions and set schedules and timelines for projects among other things.

How Program Evaluation Review Technique (PERT) Charts Work

A PERT chart uses circles or rectangles, called nodes, to represent project events or milestones. A chart can be made using different types of software. This includes specialized computer software designed to create PERT charts or even a simple program like Microsoft Excel.

The nodes on the PERT chart are linked by vectors or lines that represent various tasks. Dependent tasks are items that must be performed in a specific manner. For example, if an arrow is drawn from Task No. 1 to Task No. 2 on a PERT chart, Task No. 1 must be completed before work on Task No. 2 begins.

Items at the same stage of production but on different task lines within a project are referred to as parallel tasks. They're independent of each other and occur at the same time.

A well-constructed PERT chart looks like this:

A project manager creates a PERT chart in order to analyze all of a project's tasks while estimating the amount of time required to complete each one. Using this information, the project manager can estimate the minimum amount of time required to complete the entire project.

This information also helps the manager develop a project budget and determine the resources needed to accomplish the project.

How to Interpret a PERT Chart

A PERT chart is a visual representation of a series of events that must occur within the scope of a project’s lifetime. The direction of the arrows indicates the flow and sequence of events required.

Dotted activity lines represent dummy activities. These are items that are located on another PERT path. Numbers and time allotments are assigned and shown inside each vector. These charts have their distinct definitions and terms, the most important of which is anticipating how long it will take to finalize a project:

• The optimistic time refers to the shortest duration
• The pessimistic time is the longest it might take
• The most likely time indicates a reasonable estimate of the best-case scenario
• The expected time accounts for problems and obstacles

Advantages and Disadvantages of PERT Charts

As a project management tool, PERT charts have distinct advantages and disadvantages.

Advantages

A PERT chart allows a manager to evaluate the time and resources necessary to complete a project. It also allows the manager to track required assets during any stage of production in the course of the project.

PERT analysis incorporates data and information supplied by a number of departments. This combining of information encourages department responsibility and identifies all responsible parties across the organization.

It also improves communication during the project and it allows an organization to commit to projects that are relevant to its strategic positioning.

PERT charts are useful input for what-if analyses. Understanding the possibilities concerning the flow of project resources and milestones allows management to achieve the most efficient and useful project path.

Disadvantages

The information that goes into a PERT chart can be highly subjective. They may include unreliable data or unreasonable estimates for cost or time.

PERT charts are deadline-focused and might not fully communicate the financial positioning of a project.

Creating a PERT chart is labor-intensive, and maintaining and updating the information requires additional time and resources. Continual review of the information provided, as well as the prospective positioning of the project, is required for a PERT chart to be of value.

PERT Chart vs. Gantt Chart

The Gantt chart goes back even further than the PERT chart. American mechanical engineer Henry Gantt designed it sometime in the second decade of the 20th century and it remains the most widely used project management chart.

Like the PERT chart, the Gantt chart is a graphical depiction of a project timeline. Presented as a horizontal bar chart, it records the start and completion dates of each element of a project and indicates their interdependencies. The two charts are used in similar ways:

• Both are used to define all of the key tasks that must occur to get a project completed
• Both are useful in determining the time, money, and resources needed
• Both can be used to monitor a project's progress to completion

Early versions of the Gantt chart did not show dependencies. That is, it didn't indicate where a delay in the completion of one task could hold up the start of another task, potentially throwing a whole project off schedule. Later versions of Gantt corrected this.

Example of PERT Chart

PERT charts were first created by the U.S. Navy's Special Projects Office in the 1950s to guide the Polaris Fleet Ballistic Missile project. Using the PERT model, Navy project managers were able to:

• Evaluate the progress of their projects
• Determine the validity of their schedules
• Estimate the effects of proposed changes to the established plans

The success of this initial use of PERT charts has caused them to be used ever since in many industries.

The Bottom Line

Project management can be a very daunting and challenging task. But there are tools that managers can use to help make the process a little smoother. The PERT chart can help project managers visually map out the project's timeline by highlighting all the tasks involved. It also helps managers by laying out project instructions and the timeline needed to complete each individual task. Charts can be created using specialized computer software or even Microsoft Excel.