PERT in Project Management

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What is PERT?

A PERT chart provides a map of a project as a network diagram. A node (such as a circle or rectangle) in the diagram represents each task associated with the project. Nodes connect with arrows indicating the order of tasks and task dependencies. 

A completed PERT chart allows the entire project’s visualization, including time estimates for each task and which tasks to complete first. Teams can see potential bottlenecks and identify a critical path (the dependent task chain estimated to take the longest total time). 

PERT charts: history and goals.

The United States Navy developed the PERT chart in the late 1950s to help organize the Polaris nuclear submarine project. Now, the military, business world, and beyond use PERT charts to simplify the planning of large and complex projects.

Typically, teams create a PERT chart before a project begins to gauge its full scope, identify potential issues, and map out an appropriate timeline. This chart contrasts with another project planning tool, the GANTT chart, which organizations primarily use to monitor project progress. PERT charts also provide insights that GANTT charts often do not, including creating a clearer depiction of task hierarchies and interdependencies and estimating the entire timeline and variability.

When utilizing a PERT chart, there are four types of timelines:

  • Optimistic time: This is the shortest timeline possible for completing the project, assuming everything runs smoothly.

  • Pessimistic time: This is the longest timeline for completing the project and assumes everything that can go wrong will (but excludes general catastrophes).

  • Most likely time: This is the best estimate for how long the project will take, assuming everything proceeds as normal. 

  • Expected time: This is the best estimate overall and computed utilizing the optimistic time (O), pessimistic time (P), and most likely time (M), as follows:

Expected time = (O + 4M + P)/6

Additionally, you can calculate the variance as (P - O)/6 to estimate how much the actual time may deviate from the expected time.

Benefits of PERT charts in project management.

PERT charts enable new insights regarding project trajectories and timelines, identifying possible bottlenecks, constraints, and new opportunities for unseen efficiencies. 

Advantages of PERT charts in project management include the ability to:

  • Anticipate and address potential delays. When teams lay out the details of their projects in terms of the time for each task and interdependencies in a network diagram, it becomes easy to identify places where work may get backed up if one task fails or falls behind. By finding these problems in advance, project managers can break down tasks differently to avoid such scenarios. 

  • See opportunities for parallel workflows. While some tasks require others to be complete before they can begin, other tasks are done in parallel if enough team members are assigned. Parallel workflows can shorten the overall timeline of the project and allow teams to complete work sooner. 

  • Conceptualize tasks along the critical path. Identifying the critical path ultimately allows a project manager to determine the timescale of the entire project. The critical path is the longest chain of dependent tasks in terms of time. (In other words, it is the chain that takes the longest time to complete, not the chain with the most tasks in it.)

  • Plan for large and complex projects. While teams can visualize simple projects with simple task lists, it can quickly become difficult to keep track of everything when projects become large, involve multiple teams or departments, and the tasks within the project contain multiple interdependencies. By creating a map at the beginning, project managers can assign and prioritize tasks in a way that optimizes workflow. 

  • Enable a what-if analysis. Once the manager maps out the project, they can apply a what-if analysis, making it possible to determine outcomes that might result from any number of changes to the tasks involved. This analysis can help identify additional prospective problems and allow the project manager to identify places where greater efficiency is possible.

  • Coordinate departments more effectively. By breaking the project down by tasks, the PERT diagram allows for visualization of the role of each department or team in the larger picture, thus enabling those teams to work together more effectively by understanding how their tasks depend on each other. 

How to create a PERT chart for your project.

Here are the steps for creating a PERT chart so that you can understand the process and get started:

1. Break project milestones and goals into constituent tasks.

First, identify all major milestones or deliverables for the project. Then, break each of these down further into a list of tasks to complete to achieve the milestone. You may wish to consult the team or department leaders to make sure you don’t overlook anything.

2. Determine which tasks are prerequisites for others.

Building off the previous step, you next need to identify task dependencies. Some tasks can be completed in isolation during the project, while others are on hold until the team finishes a prerequisite task. Again, in collaboration with team leaders, identify these interdependencies. 

3. Estimate the time frame associated with each task.

Next, you need to add time estimates for each task. While you can ask those whose job it is to complete the tasks for their best estimates, people aren’t always the best judge of time frames and can be overly optimistic. Consider looking at past projects with similar tasks to get an idea of how much time each task might take. Ideally, you should note a range of possible times for each task so that you can adjust the overall timeline later on.

4. Translate your tasks and milestones into nodes.

Begin creating the chart by arranging each task and milestone on a large diagram. Nodes should represent these tasks. Note that as you begin the next step, you may need to move the nodes around, so sketching things out on a whiteboard or in a computer program will make this easier. 

5. Draw vectors between tasks.

Using your notes on task prerequisites and interdependencies, draw arrows between your nodes to indicate which tasks form dependent chains. Keep in mind that you can have parallel chains if some tasks do not affect others. You may also want to include time estimates on the nodes or the arrows connecting the nodes so that you can later estimate the entire project time. 

6. Analyze and optimize.

Once you draft your PERT diagram, look for ways to rearrange or break up tasks to optimize for time and minimize potential bottlenecks or problems. Refine your diagram until it is as clear and comprehensive as possible. 

Chart a path forward.

If you’re a project manager, you juggle many responsibilities as you plan and organize projects of varying complexity and scale. Having the right tools and knowing how and when to use them is vital. We hope the information in this article proves helpful as you expand your project management toolbox to include PERT charts.

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