PERT And CPM: An Easy Overview And Differences (2021)

Introduction

If you are in the civil engineering or construction field, you are probably familiar with PERT AND CPM. Even for project planning and control, you are supposed to know about PERT and CPM. Nowadays, they are used widely for project planning and control in large developmental projects. And so this article gives u precise knowledge of PERT and CPM. 

  1. Comparison chart
  2. Definition
  3. Pert analysis  
  4. Key differences
  5. Advantages and disadvantages

1. Comparison Chart

 

PERT 

CPM 

What Is It? 

Planning 

Technique 

Control 

Method 

 

Evolution 

Research 

Development 

Construction 

Project 

 

Focus 

Time 

Time & Cost 

2. Definition

PERT refers to Program (Project) Evaluation and Review Technique. It is generally a visual project management tool that is used in project planning.  It involves planning, organizing, integrating, and authorizing uncertain activities. It provides detailed information regarding the project’s tasks, the minimum time required for completing individual tasks, and the average time required to complete the whole project. The variable used in the PERT technique is time. The PERT Analysis shows you the critical path of a project.

The critical path is a set of activities that will cause an end date delay of the project if any one of them is not finished on time. Depending on the project, there may be more than one critical path. The Pert method includes uncertainty by making it possible to schedule a project while not precisely knowing all the activities’ details and duration. It is mostly used in projects where time is the major important factor than cost. The United States Navy first developed PERT in 1958. 

3. Pert analysis  

PERT uses a three-point estimation. They are optimistic, Most likely, and pessimistic.  

Pert method = (1×P 4×M 1×O) /6  

Here, we give more importance to the most likely. 

Also,  

PERT method = (1×P 4×M 2×O) /7  

                      = (1×P 6×M 1×O) /8 

We can also find out the standard deviation in PERT to calculate average variation.  

 Standard deviation = (O – P) /6 

To draw a PERT chart, three steps should be followed.  The first step is to draw the activities. In the second step, you need to number nodes and prioritize.  In the last step, you must add your chart’s duration to determine the critical path on that pert network. 

CPM full form is the Critical Path Method. In CPM, we are supposed to assume that the project duration is certain.  It is generally used to ascertain every activity’s earliest possible starting time.  The queue is avoided by differentiating critical and non-critical activities.  This also helps in reducing time. Any activity can be treated as a critical activity if any delay of such can delay the whole process. CPM is a project technique developed in the late 1950s by MORGAN R. It is mostly found in construction, research projects, engineering, aerospace, plant maintenance, and software development.

A CPM method developed should contain four values. There is a list of activities required to finish the project, the duration of each activity to complete, and any dependencies between the activities and milestones to be achieved. Using this, the longest path from the activities to the milestone or endpoints is found. This process also decides critical activities. It determines the least time to complete the project. 

4. Key differences

Some of the major differences between PERT and CPM are given below:  

  • PERT is a visual project management technique where we plan, schedule, organize, coordinate and control uncertain activities. Whereas CPM is a statistical technique where we plan, schedule, organize, coordinate and control well-defined activities. 
  • CPM is a method used to control cost and time. Unlike PERT, which is a technique used for planning and controlling time. 
  • PERT can be said as a development and research project tool, while CPM is a construction project tool. 
  • PERT is aligned towards events, while CPM is set according to activities. 
  • A settled model will be used in CPM.  A probabilistic model is used in the PERT method. 
  • PERT uses three-point estimations such as optimistic, most likely, and pessimistic.  Whereas on the other side, there exists only one estimate in CPM.
  • PERT is used where time is more highly valued than cost, whereas the CPM method is apt for reasonable time estimate projects.
  • PERT is used in case of unpredictable activities. On the other hand, CPM is used in the case of predictable activities.
  • PERT is used for jobs that are non-repetitive in nature. In distinction, CPM is used for jobs that are repetitive in nature.
  • There is no differentiation between critical and non-critical activities in PERT. Differentiation exists in CPM.  
  • CPM is suitable for non-research projects, while PERT is apt for research projects. 
  • The crashing technique is used in CPM while it is not used in PERT.

5. Advantages and disadvantages

A PERT chart helps you to create endpoints or milestones of the project. You can also identify any possible obstacles and quickly address them. This is the main PERT advantage. The disadvantage of PERT includes the absence of time focus. 

A CPM chart gives a precise graphical form of projects. It saves time and helps us compare our current position with the planned one. Coming to the disadvantage of CPM, it will be really hard to estimate the completion time and critical path for huge projects.  

Conclusion

The difference between PERT and CPM is reduced to a lesser degree. Nowadays, PERT and CPM are used in a complimentary way. 

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