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# Difference between PERT and CPM

Updated on 19/07/20242,213 Views

## Introduction

In the realm of project management, two popular techniques stand out for their effectiveness in planning and controlling project schedules: Program Evaluation and Review Technique (PERT) and Critical Path Method (CPM). These provide valuable insights into project timelines, activities, and dependencies, enabling project managers to streamline workflows and ensure successful project completion. In this article, we will delve into the difference between PERT and CPM in software engineering, explore their individual features, benefits, and real-life examples, and understand when to apply each technique for optimal project management outcomes.

## Overview

PERT, developed in the late 1950s by the U.S. Navy, is a probabilistic technique used to estimate project duration when there is uncertainty in activity time estimates. PERT considers three time estimates for each activity: optimistic (O), pessimistic (P), and most likely (M). By utilizing these, PERT calculates the Expected Time (TE) for each activity using the formula: TE = (O + 4M + P) / 6. PERT also focuses on identifying the critical path, which is the longest route of dependent activities determining the project's overall duration.

## Features of PERT

1. Activity Network: PERT utilizes an activity network diagram, known as a PERT chart, to depict the sequence of activities in a project. It visually represents the activities, their dependencies, and the logical flow of the project.
1. Time Estimation: PERT considers three time estimates for each activity. By combining these three, PERT calculates the expected time for each activity, taking into account the variability and uncertainty.
1. Probabilistic Approach: PERT uses a probabilistic approach to handle uncertainty in activity durations. It calculates the expected duration by assigning probabilities to the time estimates and allows for a more realistic estimation of the project timeline.
1. Critical Path Analysis: PERT identifies the critical path in a project. By analyzing this, project managers can identify the activities most critical to the project's success and focus on managing them effectively. This assists in efficient resource allocation and timely completion of critical tasks.
1. Slack or Float Calculation: PERT calculates slack or floats for each activity, which represents the amount of time a task can be delayed without affecting the project's overall duration. Slack time helps project managers identify activities that have flexibility in their scheduling and can be delayed without causing project delays.
1. Risk Analysis: PERT facilitates risk analysis by incorporating probabilistic time estimates. It allows project managers to assess the impact of uncertainties and risks on the project schedule. Managers can allocate resources and plan contingencies by identifying activities with high variability or sensitivity.
1. Resource Allocation: PERT aids in resource allocation by providing insights into activity durations and dependencies. Project managers can use this information to allocate resources effectively, ensuring that the necessary resources are available when needed to complete critical activities.
1. Progress Tracking: PERT allows project managers to track the progress of activities throughout the project lifecycle. By monitoring the actual time taken for each activity, managers can compare it with the expected time and make necessary adjustments to keep the project on track.

Overall, the features of PERT enable project managers to estimate project durations accurately, identify critical activities, manage risks, allocate resources efficiently, and track progress effectively.

## The Benefits of PERT

The benefits of PERT (Program Evaluation and Review Technique) include:

1. Accurate Time Estimation: PERT's probabilistic approach to time estimation provides a more accurate estimation of project completion time. This helps project managers set realistic expectations and plan resources accordingly.
1. Risk Analysis: PERT enables project managers to analyze and assess the impact of uncertainties and risks on project timelines. By incorporating probabilistic time estimates, PERT identifies activities with high variability or sensitivity, allowing managers to prioritize their attention and allocate resources effectively. This helps in mitigating potential risks and minimizing the likelihood of delays.
1. Resource Allocation: PERT aids in effective resource allocation by providing insights into activity durations and dependencies. By understanding the estimated time required for each activity, project managers can allocate resources efficiently, ensuring necessary resources are available when needed. This helps in optimizing resource utilization and avoiding resource bottlenecks.
1. Improved Project Planning: PERT's activity network diagram provides a visual representation of the project flow, activities, and dependencies. This aids project managers in better planning and sequencing activities, ensuring a smooth workflow. The clarity provided by PERT helps in identifying potential bottlenecks or conflicts in the project schedule, allowing for proactive measures to be taken.
1. Enhanced Communication and Collaboration: PERT facilitates effective communication and collaboration among project team members. The visual representation of the activity network diagram helps in conveying project requirements, dependencies, and timelines to all stakeholders. This fosters a shared understanding and promotes collaboration, leading to better coordination and teamwork.
1. Project Documentation: PERT provides a structured framework for documenting project activities, their interdependencies, and time estimates. This documentation serves as a valuable reference for future projects and helps in knowledge transfer within the organization. It ensures that project information is captured and can be easily accessed for planning and decision-making.

## Examples of PERT:

• Construction Project: Consider a construction project involving multiple activities such as excavation, foundation, framing, electrical, plumbing, and finishing. PERT can help estimate the project's overall duration, identify critical activities, and highlight potential delays or bottlenecks.
• Product Development: PERT can be applied in product development projects, where activities like design, prototyping, testing, and manufacturing are involved. By incorporating time estimates with uncertainties, PERT aids in project planning and resource allocation.

## The Critical Path Method (CPM)

CPM, developed in the late 1950s by DuPont and Remington Rand, is a deterministic technique used to determine the longest path of activities and the shortest project duration. It focuses on identifying critical activities that directly impact the project's total duration, enabling project managers to prioritize and allocate resources efficiently.

## Features of CPM

• Activity Sequencing: CPM utilizes a network diagram, known as a precedence diagram, to depict the logical sequence of activities. This showcases the dependencies among activities and helps visualize the critical path.
• Forward and Backward Pass: CPM employs the forward pass and backward pass techniques to calculate the early start, early finish, late start, and late finish times for each activity. These calculations aid in determining the critical path and project duration.

## What are the Benefits of CPM?

• Clear Project Timeline: CPM provides a clear understanding of project timelines, highlighting the activities critical to project completion. This knowledge enables managers to focus their efforts on critical tasks, ensuring timely project delivery.
• Resource Optimization: By identifying critical activities and their interdependencies, CPM helps project managers allocate resources effectively. It allows them to identify activities with slack time, which can be utilized to optimize resource utilization.

## Examples of CPM

• Software Development: In software engineering, CPM can be used to manage the development lifecycle. Activities such as requirements gathering, design, coding, testing, and deployment can be sequenced and analyzed using CPM to ensure efficient project delivery.
• Event Planning: CPM can assist event planners in coordinating various activities like venue selection, logistics arrangement, vendor management, and marketing. By identifying the critical path, event organizers can prioritize tasks and ensure successful event execution.

## Difference Between PERT and CPM

While PERT and CPM share similarities in their objective of project scheduling and management, they differ in their approach and usage. Here's a table highlighting the differences between PERT and CPM with examples:

 Feature PERT CPM Nature of Time Estimates Probabilistic: Considers optimistic, pessimistic, and most likely time estimates. Deterministic: Uses a single duration value for each activity, and this is a major difference between PERT and CPM in project management. Handling Uncertainty Specifically designed to handle uncertain activity durations through probability distributions. Assumes activity durations are certain and do not explicitly account for uncertainty. Focus on Critical Path Identifies the critical path and critical activities that directly impact project duration. Identifies the critical path and determines the shortest project duration. Time Estimation Formula Calculates expected time using (O + 4M + P) / 6 formula. Uses a single estimated duration value for each activity. Resource Allocation Assists in resource allocation by providing insights into activity durations and dependencies. Helps in resource allocation by identifying critical activities and their resource requirements. Risk Analysis Enables risk analysis by incorporating probabilistic time estimates. Risk analysis is not a direct focus but can be applied within the project context. Diagram Representation Uses activity network diagrams (PERT charts) to visualize project activities and dependencies. Utilizes network diagrams (CPM charts) to depict the logical sequence of activities. Example Application Research and Development Projects: e.g., Developing a new pharmaceutical drug where activity durations may vary due to uncertain research outcomes. Construction Projects: e.g., Building a residential complex where activity durations are relatively predictable, such as laying the foundation, framing, electrical, plumbing, and finishing.

## Similarities Between PERT and CPM

• PERT and CPM both focus on project scheduling and determining activity sequences and durations.
• Both techniques consider activity dependencies and utilize network diagrams to represent the project's flow.
• The critical path is identified in both PERT and CPM, highlighting the activities that impact the project's timeline.
• Both techniques facilitate project control and monitoring to track progress and make necessary adjustments.
• While the approaches differ, both PERT and CPM involve estimating activity durations.
• Resource allocation is supported by both PERT and CPM by providing insights into activity durations and dependencies.
• Project documentation is emphasized in both techniques to capture activity information for planning and decision-making

## Conclusion

In summary, both PERT and CPM offer valuable insights and techniques for effective project scheduling and management. PERT's probabilistic approach accommodates uncertainties, providing realistic project duration estimates and aiding risk analysis. CPM, with its deterministic approach, focuses on identifying critical activities and streamlining project timelines. Understanding the difference between PERT and CPM enables project managers to choose the appropriate technique based on the project's characteristics, uncertainties, and requirements. By leveraging the strengths of PERT and CPM, the professionals can enhance project planning, control, and successful execution.

## FAQs

1. How do PERT and CPM handle changes in project priorities?

PERT and CPM can adapt to changes in project priorities by reassessing activity durations, dependencies, and critical paths. Project managers can adjust the project schedule, resource allocation, and priorities accordingly to accommodate the changes.

1. How do PERT and CPM handle constraints related to resource availability?

PERT and CPM take resource availability into consideration by analyzing activity durations and dependencies. Resource allocation can be adjusted based on critical activities and supply requirements to ensure the efficient use of assets within the project constraints.

1. How do PERT and CPM handle project dependencies?

PERT and CPM both consider project dependencies by analyzing the logical relationships between activities. They identify the sequence of activities and any constraints that determine the order in which activities can be performed.

1. How do PERT and CPM account for different activity durations?

PERT accounts for different activity durations by using probabilistic estimates, considering optimistic, pessimistic, and most likely durations. CPM, however, assumes deterministic activity durations with a single estimated value.

PAVAN VADAPALLI

Director of Engineering

Director of Engineering @ upGrad. Motivated to leverage technology to solve problems. Seasoned leader for startups and fast moving orgs. Working â€¦Read More

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