All You Need To Know About PERT in Project Management

Tallyfy helps project managers track complex workflows with real-time visibility. Here is how we approach work management.

Working in project management means knowing all about several important acronym and PERT is another one that you need to be able to understand and judge whether it’s appropriate for use in your projects. Having managed software development timelines at Tallyfy, I’ve found PERT particularly useful when dealing with uncertain task durations. PERT stands for Program Evaluation and Review Technique, and it is a statistical tool created for analyzing the tasks that make up a project.

PERT in project management is often compared to the Critical Path method, which aims to fulfill a similar purpose of analyzing and representing the project tasks in a visual chart, similar to a GANTT chart. Both of these methods were created in the 1950s (while the GANTT chart dates back to the 1910s) and have become cornerstones of project management in the decades since.

Willard Fazar, head of the Program Evaluation Branch of the US Navy’s Special Projects Office, which created PERT, summed it up, saying: “Through an electronic computer, the PERT technique processes data representing the major, finite accomplishments (events) essential to achieve end-objectives; the interdependence of those events; and estimates of time and range of time necessary to complete each activity between two successive events.

The technique is a management control tool that sizes up the outlook for meeting objectives on time; highlights danger signals requiring management decisions; reveals and defines both methodicalness and slack in the flow plan or the network of sequential activities that must be performed to meet objectives; compares current expectations with scheduled completion dates and computes the probability for meeting scheduled dates; and simulates the effects of options for decision — before decision.”

What is a PERT chart?

Central to the way you use PERT is the chart, which represents the events and milestones within the project in a visual manner. Events within the process are identified via nodes (these can be either circles or rectangles) and they are linked together by lines and arrows called vectors, and it is the vectors that determine the order in which the events need to take place.

When vectors diverge from a node, that can show events that need to take place concurrently, while dotted line vectors signify events that are done in sequence but do not require resources. The following is an example of a PERT chart in the context of software development:

How do you use PERT in project management?

PERT was created to discover the time needed to complete each task necessary for the project and thus the minimum time required for completion of the whole thing. It is possible to create the chart without knowing all of the key details as it is event-focused rather than orientated around the start and completion, unlike many other project plans.

Understanding the terminology

PERT comes with several terms that you need to understand to be able to properly use it:

• PERT event - Either the start or end of an activity
• Predecessor or successor event - Events that either immediately precedes or succeed another event. All events need to be completed in sequence
• PERT activity - The performing of a task, recorded by the time taken to do so and the resources required
• PERT sub-activity - The breaking-down of activities within an activity
• Optimistic time - As the name suggests, the minimum time required to complete an activity
• Pessimistic time - And vice versa
• Most likely time - Coming somewhere in the middle of the previous two estimates, this is the best guess based on the data available but without factoring in potential problems
• Expected time - And this is the guess based on the potential for issues
• Slack - The excess time available for an activity where things can take longer than planned without causing delays
• Critical path - The longest possible route from start to finish, representing the total time allotted, so any delays beyond this will mean the project has run late

PERT step by step

• Step 1: List all the activities required - For each activity that is required to complete the project you need to estimate the length of time it will take - optimistic estimate and pessimistic estimate too - and whether it can be performed in parallel with others or done sequentially. In our conversations with project managers at engineering consultancies, we have heard that breaking down complex deliverables into phases (such as 30%, 60%, and 90% design reviews) helps create natural milestones for estimating completion. You will also need to assign it an earliest possible start date to help you plan the timeline.
• Step 2: Draw the chart - Now it’s time to create the network diagram that you will use as the PERT chart (you can also use a GANTT chart as an additional resource), either creating it by hand or through software. The most common elements used in a PERT chart are:
  • Activity
  • Duration time
  • Early start time
  • Early finish time
  • Late start time
  • Late finish time
  • Slack
  • Critical path

Example Procedure

Quarterly Strategic Planning & Goal Setting Workflow

1Revisit annual plan goals

2Break down goals into smaller chunks

3Review budget and benchmarks

4Create action steps and benchmarks

5Set expectations and timelines

+2 more steps

View template

Example Procedure

Annual Planning

1Define your goals using SMART criteria

2Build your budget and financial projections

3Set timelines and quarterly checkpoints

4Create contingency plans for when things go wrong

5Review and finalize the annual plan

View template

Example Procedure

Trade Show & Conference Planning Workflow

1Define trade show strategy and event goals

2Reserve exhibit booth space and complete registration

3Select event vendors and negotiate contracts

4Finalize booth design and marketing materials

5Assign booth staff and conduct product training

+4 more steps

View template

Advantages and disadvantages of PERT

We have already established that PERT has similarities to some other tools you can use in project management, but what are the pros and cons of selecting it over the alternatives?

PERT pros

• It makes it possible to define and visualize dependencies between the elements in the breakdown of the work.
• It enables you to identify early start, late start and slack for each activity in the project plan
• It can also offer a prediction probability for an early finish date
• Visualizing the data makes it easier to make decisions instead of being overwhelmed by it
• It helps identify the critical path in the project plan
• Using PERT in project management can help make it possible to speed up projects through better decision-making and more efficient planning of activities, thus ending the project earlier than otherwise anticipated.
• It makes it easier to manage the data and decision-making across multiple departments
• It helps create a What If analysis through different permutations and can be used as the basis for a Continuous Improvement strategy

PERT cons

• It is not easily scalable and is less helpful for smaller projects
• Printing the charts can be a challenge due to their size and complexity
• The complexity can also make it hard to analyze the findings once a project has grown significantly in size
• Using PERT in project management is less useful for measuring progress than a GANTT chart
• Subjectivity can make the data that is captured less than reliable
• Gathering the data and assembling the chart can be a time-intensive solution, so you need to know for certain that it will be useful before embarking upon it.
• More complicated projects involving multiple suppliers and activities can make it impossible to predict every eventuality, causing the PERT chart to become inaccurate

Conclusion: using PERT in project management

PERT may have been created by the US Navy as part of a nuclear submarine project, but it has become widely-used in all industries where project management is required, as Maribeth Brennan explained in 1968: “Since that time, it has been used extensively not only by the aerospace industry but also in many situations where management desires to achieve an objective or complete a task within a scheduled time and cost expenditure; it came into popularity when the algorithm for calculating a maximum value path was conceived.” Today it’s probably best used as part of a suite of project management and collaboration software tools, like GANTT charts for example. One large insurance company we spoke with manages 90-200 active construction projects simultaneously - each with complex dependencies between bid management, contract approvals, and change orders. They found that charts alone do not save you; the real challenge is orchestrating handoffs between teams when tasks have interdependencies. This helps overcome some of the disadvantages mentioned in this article, ensuring a wide-ranging and solid approach to managing the project and estimating the completion time. Employing workflow management software can help kick-start your new project, allowing for faster completion time and lower risk of mistakes. Learn how by scheduling a free demonstration!