Difference Between PERT and CPM

PERT and CPM are two statistical tools used to schedule and plan tasks or activities within a project. These methods are utilised to control time, resources, output and several other aspects of a project.

What is PERT?

PERT full form is Program Evaluation Review Technique. It is used to plan and identity the time taken to complete a particular activity in a project. Charts created via PERT provide a graphical representation of each task of a project’s timeline.

History

The US Navy Special Projects Office, The Evaluation Office of the Lockheed Missile Systems Division, and the Operations Research Department of Booz-Allen-Hamilton developed PERT back in 1957 during the production of the UGM-27 Polaris missile of the US Navy. 

Later, it was implemented in the 1968 Winter Olympics in Grenoble from 1965 until the completion of the event.

What is CPM?

The full form of CPM is the Critical Path Method. 

It is a project modelling technique that is used for scheduling project activities. It simply finds the maximum time required to complete a specific task. A CPM model includes the following – 

  • List of all activities involved in the project.

  • Dependence of each activity with one another.

  • Estimated time required to complete each activity.

History

The earliest concept of critical path was implemented by DuPont between 1940 and 1943 for the Manhattan Project, which was conducted by the US, the UK, and Canada during WWII for the production of the first nuclear weapons.

Later, Morgan R. Walker of DuPont and James E. Kelley Jr. of Remington Rand conceived CPM as a project modelling technique in the late 1950s. The attribution of CPM went to the developers of PERT, which was developed during the same time.

PERT and CPM are commonly used in conjunction with each other during project modelling.

 

Differences Between PERT and CPM

Basis for Comparing

PERT

CPM

Mode type

Probabilistic

Deterministic

Orientation

Event-oriented

Activity-oriented

Useful for

Estimating high precision time

Estimating reasonable time

Estimation

Three times

One time

Assessment of activity duration

Accurate duration of activities is not estimated 

Accurate duration of activities is estimated

Classification of activities 

Does not classify activities based on critical or non-critical nature 

Classifies activities basis critical and non-critical nature

Activity type

Unpredictable 

Predictable 

Job types

Non-repetitive 

Repetitive 

Major application 

Research and development projects 

Construction projects

Major focus 

Time 

Time-cost

Consideration for uncertainty 

Allowed

Not allowed

Common terminologies 

Slacks, network diagram, events, etc.

Float, nodes, diagram, etc. 

Crashing report 

Not applicable 

Applicable 

How to Make a PERT Chart?

  1. Identify tasks and milestones in the project.

  2. Plan activities sequentially based on milestones.

  3. Estimate the time necessary for the completion of each task. PERT Charts consider four different types of time required to accomplish a task –

  1. Optimistic time – Minimum time required.

  2. Pessimistic time – Maximum time required.

  3. Expected time – ‘Guesstimate’ of time required in case issues arise.

  4. Most likely time – Most likely time required in case there are no issues. 

  1. Determine the critical path and interpret timelines.

  2. Update the chart as the project progresses.

A PERT chart can be generated online through several websites that offer such services. Several software are also available that can create such charts. 

How to Make a CPM Chart? 

  1. Identify each activity in the project.

  2. Identify the dependencies of each activity with the other.

  3. Create the network diagram.

  4. Estimate the time required for activity completion.

  5. CPM charts consider three different times – 

  1. a - Best time.

  2. m – Most likely time. 

  3. B – Worst likely time.

  1. Identify the critical path.

  2. Modify the critical path as the project progresses.

Similar to PERT charts, CPM charts can also be generated via websites and dedicated software. 

Advantages and Disadvantages of PERT

Advantages -

  • PERT is beneficial for conducting a “what-if analysis”. By analysing the critical path, the likelihoods and different levels of uncertainties can be identified.

  • It promotes coordination among various departments of a project. This improves decision-making proficiencies and planning. Through coordination, ample data is also available that makes it easier for project management. 

  • PERT networks allow an analysis of all activities, which tell whether the project will be completed within the budget.

  • PERT displays the critical path, which identifies activities that cannot be stayed under any condition. 

Disadvantages –

  • PERT methodologies are entirely dependent on predictions, which can lead to going overboard on the estimated budget.

  • It can be less accurate to implement as there is no data available to model a project since it is only used for non-repetitive jobs.  

  • PERT is time-focused, and hence, delays in activities can lead to several issues.

Advantages and Disadvantages of CPM

Advantages -

  • CPM identifies dependencies efficiently. 

  • It can identify critical activities that are of priority.

  • CPM takes into account the resources required for a project in the most effective way.

  • Project managers can determine the precise cost and time required to complete a project. 

  • CPM offers an efficient technique to assess the procedural and technical changes that might occur.

Disadvantages –

  • CPM can be extremely complicated to implement in case of large-scale projects.  

  • Critical path identification consumes more time for projects on larger scales.

  • Creating a CPM can be time-consuming at times.

  • CPM is not effective to comply with sudden changes in the project midway.


Vedantu hopes that the above information about PERT and CPM is helpful for all commerce students. Make sure to check out our website for more articles and blogs related to different subjects, topics, and more. 

FAQ (Frequently Asked Questions)

1. What is PERT?

PERT or Program Evaluation Review Technique is a methodology used to identify the time taken for completion of a particular activity within a project.

2. What is CPM?

CPM or Critical Path Method is a statistical tool used for scheduling project activities. It funds the maximum time required for the completion of a specific task.

3. Where is PERT Useful?

PERT is useful in research and development projects that are unpredictable and uncertain.

4. Where is CPM Useful? 

CPM is useful for construction projects that are predictable and certain.

5. Are PERT Charts More Advantageous than Gantt Charts? 

PERT charts are considered more advantageous than Gantt charts owing to the former’s ability to identify task dependencies.