About PERT and CPM in Detail
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 identify 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.
Steps involved in CPM
The program manager has to list all the tasks involved in finishing the entire project.
Then he has to determine and note down the order of the events and draw a flowchart or diagram of the events.
Then he has to pick the tasks that might take more time or critical time to finish and then determine other tasks that are dependent on these tasks
He has to regularly update the diagram as the project progresses.
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
How to make a PERT Chart?
Identify tasks and milestones in the project.
Plan activities sequentially based on milestones.
Estimate the time necessary for the completion of each task. PERT Charts consider four different types of time required to accomplish a task –
Optimistic Time – Minimum time required.
Pessimistic Time – Maximum time required.
Expected Time – ‘Guesstimate’ of time required in case issues arise.
Most likely Time – Most likely time required in case there are no issues.
Determine the critical path and interpret timelines.
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?
Identify each activity in the project.
Identify the dependencies of each activity with the other.
Create the network diagram.
Estimate the time required for activity completion.
CPM charts consider three different times –
a - Best time.
m – Most likely time.
B – Worst likely time.
Identify the critical path.
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.
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FAQs on Difference Between PERT and CPM
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. It was developed by the US navy in 1957 and it is used to determine the minimum time required to finish a task or job. On the other hand, this technique determines the shortest time that the activity would take, the minimum time or the possible time and the longest time the task would take to finish. It helps the program heads and managers to know the status of different tasks in the program and the time that would be taken to finish the program. When the program manager gets to know the minimum time of each task, he would estimate the entire time taken to finish the whole project and this will help in setting realistic targets and schedules. Two important steps in PERT methodology are, optimistic time which measures the minimum time that a task would take to finish and pessimistic time which measures the maximum time that would be taken to finish a job. On the other hand, most likely time is the time taken to finish the task if everything goes as planned. The final step would be calculating the PERT estimate.
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. It was developed by the US navy in 1957 and it is used to determine the minimum time required to finish a task or job. On the other hand, this technique determines the shortest time that the activity would take, the minimum time or the possible time and the longest time the task would take to finish. It helps the program heads and managers to know the status of different tasks in the program and the time that would be taken to finish the program. When the program manager gets to know the minimum time of each task, he would estimate the entire time taken to finish the whole project and this will help in setting realistic targets and schedules. Two important steps in PERT methodology are, optimistic time which measures the minimum time that a task would take to finish and pessimistic time which measures the maximum time that would be taken to finish a job. On the other hand, most likely time is the time taken to finish the task if everything goes as planned. The final step would be calculating the PERT estimate.
3. Where is PERT useful?
PERT is useful in research and development projects that are unpredictable and uncertain. This technique determines the shortest time that the activity would take, the minimum time or the possible time and the longest time the task would take to finish. It helps the program heads and managers to know the status of different tasks in the program and the time that would be taken to finish the program. When the program manager gets to know the minimum time of each task, he would estimate the entire time taken to finish the whole project and this will help in setting realistic targets and schedules. Two important steps in PERT methodology are, optimistic time which measures the minimum time that a task would take to finish and pessimistic time which measures the maximum time that would be taken to finish a job. On the other hand, most likely time is the time taken to finish the task if everything goes as planned.
4. Where is CPM useful?
CPM is useful for construction projects that are predictable and certain. The program managers need to have a CPM for every project because every project has risks that would delay the targets. The goal of this method is to find out the critical time taken to finish the target so that one could mobilise the resources better. This helps the manager to understand which tasks are on CPM and needs some special attention of human resources to finish it and also helps in bringing out the best practices to finish these targets on time. It also helps in making realistic targets and schedules the next time when they plan for another project. This method includes drawing a graph of every activity in the entire project and determining the time taken to finish them, finally highlighting the tasks that would take longer time than the rest.
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.
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