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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.
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.
PERT in Project Management:
Program Evaluation and Review Technique (PERT) is a project management tool used to analyze and represent the tasks involved in completing a project. PERT is ideal for projects with uncertain task durations. It calculates the expected time for each task using three estimates: optimistic, pessimistic, and most likely. These estimates help identify the critical path and assess the project's potential timeline, allowing for more informed decision-making and risk management.
CPM in Project Management:
The Critical Path Method (CPM) is a project management technique used to schedule project activities. CPM focuses on determining the longest sequence of dependent tasks (critical path) that dictates the minimum project duration. It helps project managers prioritize resources and identify task dependencies to avoid delays. Unlike PERT, CPM assumes fixed task durations.
Example of Construction Project through PERT and CPM
Tasks:
Site Preparation (A) - 3 days
Foundation (B) - 5 days (depends on A)
Wall Construction (C) - 6 days (depends on B)
Roof Construction (D) - 4 days (depends on C)
Electrical Work (E) - 3 days (depends on C)
Final Inspection (F) - 2 days (depends on D and E)
PERT (Program Evaluation and Review Technique) Example:
For each task, use optimistic, pessimistic, and most likely time estimates:
Task A: \[ O = 2, \quad M = 3, \quad P = 4 \] \[ TE = \dfrac{O + 4M + P}{6} = \dfrac{2 + 4 \times 3 + 4}{6} = 3 \text{ days} \]
Task B: \[ O = 4, \quad M = 5, \quad P = 6 \] \[ TE = \dfrac{O + 4M + P}{6} = \dfrac{4 + 4 \times 5 + 6}{6} = 5 \text{ days} \]
Task C: \[ O = 5, \quad M = 6, \quad P = 7 \] \[ TE = \dfrac{O + 4M + P}{6} = \dfrac{5 + 4 \times 6 + 7}{6} = 6 \text{ days} \]
Task D: \[ O = 3, \quad M = 4, \quad P = 5 \] \[ TE = \dfrac{O + 4M + P}{6} = \dfrac{3 + 4 \times 4 + 5}{6} = 4 \text{ days} \]
Task E: \[ O = 2, \quad M = 3, \quad P = 4 \] \[ TE = \dfrac{O + 4M + P}{6} = \dfrac{2 + 4 \times 3 + 4}{6} = 3 \text{ days} \]
Task F: \[ O = 1, \quad M = 2, \quad P = 3 \] \[ TE = \dfrac{O + 4M + P}{6} = \dfrac{1 + 4 \times 2 + 3}{6} = 2 \text{ days} \]
Critical Path: A → B → C → D → F → Total time = 3 + 5 + 6 + 4 + 2 = 20 days
CPM (Critical Path Method) Example:
For CPM, durations are fixed:
Task A: 3 days
Task B: 5 days (depends on A)
Task C: 6 days (depends on B)
Task D: 4 days (depends on C)
Task E: 3 days (depends on C)
Task F: 2 days (depends on D and E)
Critical Path: A → B → C → D → F
Total time = 3 + 5 + 6 + 4 + 2 = 20 days
Key Takeaways:
PERT estimates task durations probabilistically and helps manage uncertainty.
CPM uses fixed durations and identifies the critical path to minimize project duration.
Both methods yield the same result in this example: 20 days.
FAQs on Difference Between PERT and CPM
1. What is the main difference between PERT and CPM?
PERT is probabilistic, focusing on estimating uncertain task durations, while CPM is deterministic, using fixed durations to identify the critical path.
2. When is PERT used?
PERT is used for projects with uncertain or unpredictable task durations, such as research and development projects.
3. What type of project is CPM best suited for?
CPM is ideal for construction or manufacturing projects, where task durations are predictable.
4. What are the key components of a PERT chart?
PERT charts include tasks, their estimated times (optimistic, pessimistic, most likely), and their dependencies.
5. What is the purpose of the critical path in both methods?
The critical path determines the longest sequence of dependent tasks, dictating the minimum time required to complete the project.
6. Can PERT be used for repetitive tasks?
No, PERT is generally not used for repetitive tasks as it is designed for non-repetitive, uncertain projects.
7. Does CPM allow for uncertainty in project tasks?
No, CPM does not account for uncertainty, as it uses fixed task durations.
8. How do PERT and CPM handle task dependencies?
Both methods involve identifying task dependencies, but PERT focuses on estimating durations under uncertainty, while CPM focuses on scheduling based on fixed times.
9. Can PERT and CPM be used together?
Yes, both methods can be used together, especially in large projects where both uncertainty and fixed durations exist.
10. Which method is better for cost estimation?
CPM is generally better for cost estimation as it factors in resource allocation and time-cost relationships, whereas PERT focuses mainly on time management.
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