How do you effectively use PERT analysis for project scheduling?

1 What is PERT analysis?

PERT analysis is based on the idea that the actual time required to perform a task can vary depending on various factors, such as resource availability, dependencies, risks, and quality standards. Therefore, instead of using a single time estimate for each task, PERT analysis uses three time estimates: optimistic, pessimistic, and most likely. The optimistic time estimate is the shortest possible time to complete the task, assuming everything goes smoothly. The pessimistic time estimate is the longest possible time to complete the task, assuming everything goes wrong. The most likely time estimate is the most realistic time to complete the task, based on past experience and current conditions. PERT analysis then uses a formula to calculate the expected time for each task, which is a weighted average of the three time estimates.

2 How to calculate the expected time for each task?

The formula for calculating the expected time for each task is:

Expected time = (Optimistic time + 4 x Most likely time + Pessimistic time) / 6

This formula gives more weight to the most likely time estimate, as it reflects the most probable scenario. The optimistic and pessimistic time estimates are used to account for the uncertainty and variability of the task duration. The expected time for each task is then used to construct a network diagram, which shows the sequence and interrelationships of the tasks in the project.

3 How to identify the critical path?

The critical path is the longest path of tasks in the network diagram, which determines the minimum time required to complete the project. The critical path can be identified by adding up the expected times of the tasks along each path, and finding the path with the highest total. The tasks on the critical path are called critical tasks, and they have zero slack or float, which means they cannot be delayed without affecting the project's completion date. The tasks that are not on the critical path are called non-critical tasks, and they have some slack or float, which means they can be delayed up to a certain amount without affecting the project's completion date.

4 How to calculate the slack or float for each task?

The slack or float for each task is the difference between the latest and the earliest possible start or finish times for that task. The latest start or finish time for a task is the latest time that the task can start or finish without delaying the project's completion date. The earliest start or finish time for a task is the earliest time that the task can start or finish without affecting the start or finish times of its predecessors or successors. The slack or float for each task can be calculated by using the forward and backward pass methods, which involve tracing the network diagram from left to right and from right to left, respectively, and applying the following formulas:

Latest start time = Latest finish time - Expected time

Latest finish time = Minimum of the latest start times of the successors

Earliest start time = Maximum of the earliest finish times of the predecessors

Earliest finish time = Earliest start time + Expected time

Slack or float = Latest start time - Earliest start time

5 How to use PERT analysis for project scheduling?

PERT analysis can help you create a realistic and flexible project schedule, providing the expected time, critical path, and slack or float for each task. With this information, you can allocate resources and assign priorities to the critical tasks, monitor and control the progress of the project, communicate and report the status and risks to stakeholders, as well as adjust and update the project schedule. For example, you can compare the actual time with the expected time to identify any deviations or delays that may affect the critical path. Additionally, you can use network diagrams and PERT charts to graphically represent tasks, dependencies, and time estimates. Finally, you can revise time estimates, add or remove tasks, or change sequence or dependencies of tasks as new information becomes available.

6 What are the benefits and limitations of PERT analysis?

PERT analysis offers several advantages for project scheduling, such as accounting for the uncertainty of task duration, identifying the critical path and tasks, optimizing resource use, and improving communication and collaboration. However, it can be complex and time-consuming to apply, especially for large projects. It can also be inaccurate or unreliable if the time estimates are based on subjective judgments or insufficient data. Additionally, it can be misleading or unrealistic if it ignores external factors that may affect the project, and inflexible if it does not allow for changes in the project scope, quality, or risk.