PERT Chart in a Nutshell
PERT allows you to pinpoint the start and due dates and reduce the costs and time needed to complete a project!
PERT Chart vs. Gantt Chart
Both these tools are visual and help managers work on large projects. However, the purpose of their initial invention makes them adapt to different stages and types of projects. Find out which of these tools best fits your needs!
Tasks are displayed in a network diagram
Linear presentation of tasks and timelines
Useful in the planning stage of the project
Best suited for monitoring the development of projects
Developed for managing complex projects by the US Navy in the 1950s
Developed for visualizing tasks by Henry Gantt in the 1910s
Highly flexible and adaptable
Outlines and calculates the critical path
Focused on task duration, dependencies, and timeline
Pert Chart Definition
The Program Evaluation Review Technique, commonly known as PERT, is a visual tool in project planning that helps organizations analyze and represent the activity and evaluate and estimate the time required to complete the project within deadlines. PERT allows planners to identify start and end dates and ultimately reduce costs and time needed to complete the project.
PERT was developed in 1958 by the US Navy as part of the Polaris Project. They aimed to manage the Polaris submarine missile program. At around the same time, an American chemical enterprise El DuPont de Nemours devised a similar approach called the Critical Path Method (CPM). Unlike CPM, which determines the longest path to complete a project, PERT gives you three different time estimates. While CPM focuses on time, PERT focuses on the time-cost trade-off.
PERT in 5 Steps
PERT charts are very useful in the planning stage of projects, so managers can identify the best-case and the worst-case scenarios. While it's impossible to predict the future, learning how to create one of these templates in five steps can help you in the planning process.
Step 1: Identifying specific milestones— By listing all your tasks in the table, you get a clear overview of all the steps, which you can subsequently expand by adding information on sequence and the time necessary to complete each activity.
Step 2: Determining the sequence of activities— While it is easy to predict the order of some activities, other tasks may require more in-depth analysis, which will help you determine their order more easily.
Step 3. Constructing a network diagram— Once you have established the sequence of activities, you can represent both serial and parallel activities in the diagram. Each event and milestone should represent a node in the network, and you can use arrows to show relationships between activities.
Step 4: Estimating the time necessary for each activity— What distinguishes PERT from other techniques is its ability to deal with uncertainty in activity completion time. There are three-time estimates this model typically uses for each activity:
• Optimistic time - the shortest time in which the activity can be completed
• The most likely time - the completion time that has the highest probability
• Pessimistic time - the longest time in which the activity can be completed
After you have identified the time estimates, you can calculate the expected time for each activity by using the following weighted average:
Expected time = ( Optimistic + 4 x Most likely + Pessimistic) / 6
For example, imagine you are building a cottage. Drilling and planting the posts have an optimistic duration of 7 hours, an expected duration of 10 hours, and a pessimistic duration of 12 hours. The optimistic duration is counted once, the most likely time is counted four times, and the pessimistic time is counted once. The entire sum is then divided by 6, and the weighted average is 9,83. You perform this calculation for each event and then share it by inserting it into the duration data column.
Step 5: Identifying the critical path— By adding the times for the activities and determining the longest path, you create a critical path. The critical path involves the total amount of time necessary to complete the project. The total project time doesn’t change if activities outside the critical path speed up or slow down.
PERT Chart in Project Management
PERT helps project managers identify responsible departments, delegate roles to their team workers, and track results. Gathering information from multiple sources allows you to coordinate project activities and leverage communication between departments easily. Through efficient planning and decision-making, you encourage your team to truly invest their time and energy into delivering the best results.
Interpretation of a PERT Chart
We already compared PERT and Gantt charts, but we need to put them one beside the other once more. Gantt charts are linear, and you'll notice that one task is dependent on the other, creating a chain of events that lead to the project finish line. PERT charts are a little bit more complicated and can look confusing at first, so let's try to break down the most common dilemmas!
The "boxes" represent project milestones and are also called nodes.
The nodes are connected by lines that represent the tasks that need to be completed so that you can hop from one milestone to the next.
The lines that connect the nodes are in the form of arrows so they can indicate the order in which the dependent tasks must be completed. For example, you can't start creating a website before getting all the necessary information and files from the client.
The numbers written by the arrows display the amount of estimated time it takes to complete the tasks from one milestone to the other.
Sometimes, you'll see two diverging lines coming out of one node and reaching two different nodes. This means you have parallel tasks. They are activities that are independent of one another, happen simultaneously, and are also known as concurrent tasks.
Pert Chart Example
We’ll follow the template described above to illustrate the example of going on vacation. So, you’ll need to list all the necessary activities. In our example, those would be: booking a flight and accommodation, researching interesting places to visit in the area, doing the math on how much money you need, getting days off, packing, agreeing with your travel companions on the dates and destination, and choosing the destination. Naturally, these activities need to be put in the right order, meaning you’ll probably agree with others on the destination first and pack in the end.
Then, you’ll use software to create a diagram and represent these activities as nodes. You’ll also create dependencies by connecting them with arrows, which will give you a clear idea of the activity sequence. Schedule your tasks and give them a time estimate, so you can then calculate their optimistic and pessimistic versions. Finally, create a critical path, add up the estimated times of the tasks on it, and you’ll know how much time it will take you to complete the project of going on vacation and the necessary steps you need to take.
Although PERT makes you clearly define all the activities on a project, it’s sometimes impossible to predict every step. Changes happen during the project, and they can seriously affect the initial PERT. While it’s possible to modify tasks in any software, it takes a lot of time and energy without contributing much to the project.
Project managers make time estimates and since they heavily depend on judgement, the numbers are only guesses, especially if the project manager has little experience with the activities at hand.
At its core, PERT allows you to control complex and ambitious projects whose objectives can be highly critical. It helps you determine the fastest possible route to complete the projects.
PERT gives you a number of benefits:
• In-depth analysis of project activities by viewing the activities both independently and in connection with each other, you get a clear view of the time and the budget required to finish the entire project.
• What-if analysis helps you identify all the possibilities and uncertainties related to the project. By trying different combinations and choosing the most useful possibility, you eliminate the risk of having project surprises. Also, it helps you highlight the activities that require careful monitoring.
Overall, PERT allows you to have an idea of possible time variation and helps you assess the importance of problems you have to face along the way. Unlike most methods, PERT gives you the flexibility to identify the best-case and the worst-case scenarios and develop a strategy on how to best coordinate large-scale projects.
PERT is also a very helpful visual tool that lets you see in the form of a diagram all the necessary tasks and their dependencies that must be completed for the project to be successful. This is a very handy tool when planning a project and can be used to distribute resources and present estimates to stakeholders.