Control Techniques: PERT and CPM

Control Techniques are used to plan, monitor, and evaluate the progress of various activities. Among the many quantitative techniques, PERT (Program Evaluation and Review Technique) and CPM (Critical Path Method) are two widely adopted tools in project and operations management. These techniques are essential for time management, resource allocation, and overall control of large-scale, complex projects.

Program Evaluation and Review Technique (PERT)

PERT is a project management technique used for planning and controlling time for complex and non-repetitive projects. It was developed in the 1950s by the U.S. Navy for the Polaris missile project. It is particularly suitable for research and development (R&D) or defense-related projects where the time required for tasks is uncertain.

PERT is event-oriented, which means it focuses on milestones (events) instead of activities. It uses probabilistic time estimates to handle uncertainty in project scheduling. In PERT, each activity duration is estimated using three time values:

• Optimistic time (O): Minimum time to complete the task

• Pessimistic time (P): Maximum time to complete the task

• Most likely time (M): Best estimate of time considering normal problems

The expected time (TE) is then calculated using the formula:

TE = (O + 4M + P) / 6

This approach helps managers plan more realistically by accounting for possible time variations.

Uses of PERT:

• Planning of Uncertain Projects

PERT is used where activity durations are not known with certainty, such as in research, innovation, or construction projects. It helps managers anticipate delays and prepare for contingencies, making it suitable for non-routine, high-risk projects.

• Scheduling and Sequencing

PERT helps determine the sequence of tasks and identifies dependencies between them. It clearly outlines which tasks must be completed before others begin. This enables effective project scheduling.

• Time Management and Deadline Control

By identifying the critical path, PERT shows the longest sequence of dependent activities and their total project duration. This helps managers focus on critical tasks that affect project completion and avoid delays.

• Risk Analysis and Forecasting

Since PERT incorporates time estimates and standard deviation, it enables quantitative risk analysis. Managers can calculate the probability of completing the project within a specific time frame, aiding in decision-making under uncertainty.

• Improved Coordination

PERT provides a visual network diagram showing interdependent activities and timelines. This enhances coordination among departments, as everyone understands their roles and timelines, leading to better team collaboration.

• Progress Monitoring and Control

PERT allows for ongoing evaluation by comparing actual progress with planned timelines. Managers can identify delays early and take corrective actions, thus improving project control and ensuring timely completion.

Critical Path Method (CPM)

CPM is a deterministic project management technique developed in the late 1950s by DuPont. It is used primarily for construction, engineering, and manufacturing projects where activity durations are relatively predictable. Unlike PERT, which is event-oriented, CPM is activity-oriented, focusing on the duration and sequence of tasks.

In CPM, each activity has a fixed time estimate and is analyzed to determine the critical path—the longest path through the network with the least amount of scheduling flexibility (zero float). The critical path determines the shortest possible duration of the entire project.

The goal of CPM is to identify tasks that must not be delayed and ensure resource allocation and scheduling align to prevent overall project delays.

Uses of CPM:

• Project Planning and Scheduling

CPM is an essential tool in project scheduling, helping to identify task sequences and dependencies. It provides a structured timeline and helps visualize the start and end dates of activities, ensuring efficient time planning.

• Identifying the Critical Path

The critical path includes tasks that directly impact the overall project duration. Any delay in these activities causes a delay in the entire project. Identifying this path helps managers prioritize resources and attention accordingly.

• Resource Allocation

CPM allows for effective resource planning by showing which tasks can be delayed without affecting the project. This helps in reallocating manpower, machinery, or funds from non-critical to critical tasks, improving operational efficiency.

• Time-Cost Trade-Off Analysis

One of CPM’s strengths is crashing, where the project duration is shortened by speeding up activities at additional cost. Managers can use CPM to evaluate the trade-off between time and cost, choosing the best balance to meet deadlines within budget.

• Performance Measurement and Monitoring

CPM serves as a control mechanism by comparing actual vs. planned progress. Any deviations can be quickly spotted, and corrective steps can be taken. It improves project transparency and accountability.

• Repetitive Projects

CPM is ideal for routine and repetitive projects, such as factory construction or infrastructure development, where time estimates are fixed. It provides a reliable and predictable framework for project completion.

Key differences between Comparison of PERT and CPM