Difference Between Pert and CPM

A project can only be managed successfully through timely planning and effective control. Two popular management techniques are PERT (Program Evaluation and Review Technique) and CPM (Critical Path Method). PERT and CPM are methods used to divide a project into tasks, estimate their time, and create an organized project schedule. PERT is applicable when durations are uncertain, while CPM can be used when times are fixed.  Both concepts help you avoid delays and help better manage your resources.  This blog will explain and help you explore PERT and CPM, how they work, and when you might use them, their steps, the benefits of each, their differences, and common errors in detail.

Table of Contents:

• What is the Project Evaluation and Review Technique (PERT)?
• Advantages and Disadvantages of the PERT Chart
• Steps to Create a PERT Chart
• What is the Critical Path Method (CPM)?
• Advantages and Disadvantages of the Critical Path Method
• Steps to Find the Critical Path Method in a Project
• Difference Between PERT and CPM
• Common Mistakes in PERT and CPM Implementation
• Practical Use Cases of PERT and CPM
• Conclusion

What is the Project Evaluation and Review Technique (PERT)?

Project Evaluation and Review Technique (PERT) uses three time estimates for each task: the optimistic time, the most likely time, and the pessimistic time to make its estimate of the expected time to complete a task. The main purpose of PERT is to identify the critical path. The critical path is the longest sequence of dependent tasks that must be finished on time to keep the project on schedule. Knowing these tasks helps the project manager focus only on activities that could delay the project.

Importance of PERT in Project Management:

There are multiple benefits of using a Project Evaluation Review Technique for planning and scheduling a project:

1. Helps identify the critical path: The critical path demonstrates the longest string of dependent tasks. If delayed, that string of tasks will delay the whole project. PERT charts help demonstrate this relevant path for the project managers.
2. Better planning and coordination of tasks: The PERT chart will show what tasks must be completed before other tasks can begin. This will help to minimize task confusion and coordination.
3. Minimizes project risks: By visualizing all paths in a project and estimating time wisely, PERT techniques can limit the amount of unexpected delays in project management. 
4. Improves Resource Management: PERT helps project managers understand which tasks need more attention and more resources.
5. Enhances decision-making: With a clear overview of task dependencies and timelines, project managers can make informed decisions to keep the project on track.

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Advantages and Disadvantages of the PERT Chart

Like any other project management tool, there are advantages and disadvantages to a PERT chart. A PERT chart improves planning, scheduling, and coordination of tasks, but has some limitations depending on the size of your project and the confidence in the task estimates. Let’s take a look at the major advantages and disadvantages of utilizing a PERT chart.

Advantages of the PERT Chart

Let’s explore the advantages of the PERT Chart:

• More Accurate Time Estimates: In each task, PERT assigns three time estimates, which gives a clearer picture of the task’s duration.
• Identifies Task Relationships: It demonstrates task relationships, allowing you to see which tasks must be completed first and which tasks can start after. This will help your team stay on track.
• Focuses on Key Tasks: PERT will assist the manager in locating the critical path, which means they can focus on the critical tasks that impact the project’s completion timeline.
• Enhances Project Planning: It provides a complete overview of the project, making it easier to plan for each step accurately and mitigating the risk of delays.

Disadvantages of the PERT Chart

Let’s explore the disadvantages of the PERT Chart:

• Takes Time to Create: Implementing a detailed PERT chart that includes time estimates and task dependencies can be labor-intensive.
• Estimates May Be Inaccurate: The time estimates in PERT depend on subjective assumptions. It simply takes one incorrect assumption, and the whole schedule is at risk.
• Not Good for Simple Projects: Small or simple projects often do not need a PERT chart; the details can be over the top.
• Can Get Complicated: In extremely large projects with a multitude of tasks, reading and managing the chart can be challenging.

Steps to Create a PERT Chart

Let’s explore the steps required to create a PERT Chart:

Step 1: List Activities for the PERT Chart

The first step is to list all tasks required to complete the project, each with a clear start and end point. This breaks the project into smaller parts that are easier to understand and manage. At this stage, focus on identifying all activities needed to finish the project, without worrying about their order.

Step 2: Identify Activity Dependencies in the PERT Chart

After you have a completed list of tasks, the second step is to identify how the tasks are related. Some tasks can only start after another task is finished. These are called dependent tasks. For example, you cannot begin testing a product until you have built it first. As a result of identifying these relationships among the tasks, you will be able to properly sequence the tasks as they relate to the project. This will provide you with an understanding of the flow of work through the project.

Step 3: Assessing Task Duration by using PERT

Once you have identified the dependencies, you’ll need to estimate how long it will take to do each task. In PERT, this is accomplished by utilizing three time estimates. These are the optimistic time, which is the shortest time for the task to be completed, most likely time, which is the expected time for the task to be completed, and pessimistic time, which is the longest length of time for the task to be completed if you experience delays. These values help you calculate the expected time for each task, which will help your time estimates be more accurate and realistic. 

Step 4: Calculate the Critical Path on the PERT Chart

Once you have your time estimates, you can now begin to construct your PERT chart. Connect the tasks according to their dependencies and show the expected time for each. Once you are done, you can identify your critical path. The critical path is the longest path from the start of the project to the end. The critical path must be done on time. If any of the tasks on the critical path are late, the entire project will be late. Determining your critical path keeps your project focused on the most critical tasks.

Step 5: Monitor and Control Progress using PERT

Once the PERT chart is created, it serves as an important tool for tracking the performance of the project. You should use it to determine if the work is progressing as planned. If any of the critical path tasks are not completed on time, you’ll know corrective action is necessary. And, as the project moves on, you can also modify the chart, which will help keep you better informed about the schedule and allow for plan changes.

What is the Critical Path Method (CPM)?

The Critical Path Method (CPM) is used to plan and manage projects. It helps organizations identify the most critical tasks that must be completed on time, ensuring the entire project is not delayed. These important tasks are referred to as “critical tasks.” If any of them are late, the entire project will be delayed. Project managers use CPM to see which tasks need the most focus and more planning to complete them. It also makes sure that the project is completed on time.

Importance of CPM in Project Management

Let’s explore the importance of CPM in Project Management:

1. Better Scheduling: It helps in making a clear project timeline.
2. Identifies Critical Tasks: It helps in identifying which task is important.
3. Helps Avoid Delays: It helps project managers take action in advance to prevent delays.
4. Improves Resource Use: It allows better planning of workers, materials, and tools.
5. Good Communication: It promotes clear interaction among team members, helping everyone understand the tasks better.

Advantages and Disadvantages of the Critical Path Method

Like any other project management tool, the Critical Path Method offers both advantages and disadvantages. It helps in improving planning and tracking, but it also has some challenges, particularly in larger or more uncertain projects. Let’s take a look at the main advantages and disadvantages of using CPM.

Advantages of the Critical Path Method

Let’s explore the advantages of the Critical Path Method:

• Transparency in Project Timeline: CPM indicates how much time the project will take and which tasks matter most. 
• Aiding Planning and Monitoring: CPM allows managers to plan and monitor the tasks easily.
• Increases Productivity: Resources can be employed better because of an emphasis on the critical tasks.
• Improved Decision Making: CPM supports good decisions by explaining the tasks with priority.

Disadvantages of the Critical Path Method

Let’s explore the disadvantages of the Critical Path Method:

• Requires Detailed Planning: It requires a listing of all the tasks with their time estimates. This can take a lot of time and effort.
• Can Be Complicated in Larger Projects: The CPM becomes harder to manage when a project contains too many tasks.
• Little Flexibility for Unplanned Changes: CPM works well when your planned project goes as expected, but it does not plan for unforeseen changes very well.
• Time-Consuming to Maintain: CPM works very well when there are no changes and everything goes as planned, as it doesn’t allow sudden changes.

Steps to Find the Critical Path Method in a Project

Let’s explore the different steps required to find the Critical Path Method:

Step 1: Creating a list of activities for the Critical Path Method 

To begin, you will need to compile a list of all the activities to be completed to finish the project from start to finish. These are called project activities. To collect this list, you can review the project plan, interview team members, or decompose the work into smaller portions using a Work Breakdown Structure (WBS). The activities should be listed in an unambiguous manner so that everyone will know what to expect. For example, in the construction example, the activities would include: lay foundation, put up walls, install windows, paint the house, etc. Every step matters, so don’t skip any step, even if it’s a small one.

Step 2: Finding dependencies for the Critical Path Method

With your list of activities created, the second step is to determine how the activities are linked together. Some activities cannot start until others are finished. These links between activities are called dependencies.

For example, you will not be able to paint the house until the walls are up. It is important to understand if the activities must be completed in the correct sequence or whether they may be completed in parallel. This will allow you to determine the appropriate sequence to complete the project. 

Step 3: Draw a Network Diagram for the Critical Path Method

Once the order of work is known, the next step is to create a network diagram. A network diagram is a visual chart that shows the project tasks and how they depend on each other. Each task is shown inside a box or circle, and arrows connect them to illustrate the correct sequence. The diagram starts with the first task and ends with the last one. This visual map helps everyone on the team understand the flow of activities and how each task relates to the next. It also serves as a useful tool for later calculating the project’s critical path.

Step 4: Estimate Task Duration Using Critical Path Method

Next, you will need to determine how much time will be required to complete each task. Depending on the size of the project, you can estimate your duration in hours, days, or weeks. Be as accurate as possible. You can estimate time based on the seasoned experience of the team, professional advice, or prior projects with similar tasks or activities.

Example:

• Design homepage: 4 days
• Write content: 3 days
• Build backend: 5 days
• Test website: 2 days
• Launch website: 1 day

These estimated time values help determine the overall project duration by considering all the individual tasks.

Step 5: Calculate the Critical Path Method

This is the last step, but may be the most important. You now have a list of tasks, the order of work, and how long each will take to complete, so now you can calculate the Critical Path. 

Here is how: 

List all possible paths through the network from start to finish. Add up the time for each path by adding the duration of each task in that path. The path with the longest total time is your Critical Path. The tasks in this path will be at the top of your priority list. If any of these tasks are delayed or fall behind schedule, then the entire project is delayed. The point is, once you have the Critical Path, you can focus on the critical tasks to be sure they all stay on task.

Difference Between PERT and CPM

Common Mistakes in PERT and CPM Implementation

Let’s explore the common mistakes people make while implementing PERT and CPM:

• Inaccurate Time Estimations: If the time is too short or too long, the plan may not work accurately, which can cause delays or waste of time and resources.
• Skipping Task Dependencies: Some tasks depend on others. If these connections are not properly shown, the schedule can become confusing.
• Overlooking Critical Path: The critical path in CPM is the longest sequence of tasks that needs to be executed on time. Ignoring or not updating the critical path could cause you to miss the project deadline.
• Not Updating the Plan: Due to delays or the addition of new tasks, projects always keep changing. If you don’t update your PERT or CPM chart, it becomes very old and no longer useful.

Practical Use Cases of PERT and CPM 

PERT and CPM are valuable techniques used in many industries to manage large and complex projects. Listed below are some real examples of how these uses can be applied in the following industries: 

• Construction Industry: For capital projects such as building roads, bridges, and office buildings, CPM is useful for planning the sequence of work and managing manpower and time. PERT is helpful when project tasks involve uncertainty, like obtaining permits or delivering materials.
• Software Development Industry: In software projects, PERT helps estimate the time needed for uncertain tasks like coding, testing, and debugging. CPM is used to track progress and plan key milestones to prevent delays.
• Event Planning: For events like weddings, conferences, or company meetings, PERT and CPM assist in organizing logistics, assigning responsibilities, and ensuring all preparations finish on time.
• Research and Development (R&D): In new product development or scientific research, some tasks have uncertain durations. PERT helps plan for these unknowns, while CPM identifies critical steps to complete the project within the deadline.

Conclusion

Both PERT and CPM are essential project management techniques that bring structure, clarity, and control to complex projects. PERT is especially helpful for estimating tasks with uncertain durations, while CPM excels at tracking dependencies and managing deadlines. While both tools are powerful, project managers must avoid common mistakes like inaccurate time estimates and neglecting regular updates. When used correctly, these methods lead to better planning, more efficient resource use, and a higher chance of project success. Whether you work in construction, IT, event planning, or research, applying PERT and CPM can significantly enhance how you manage and deliver projects.

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