PERT and CPM

Abstract

Program Evaluation and Review Technique, known as PERT, is a powerful tool used by project managers to plan and execute complex projects. PERT breaks down complicated projects into smaller and more tangible tasks and develops a network diagram with the tasks. The network diagram describes the relation and dependencies between each task and durations for each individual task is estimated. The time estimate of tasks can be calculated through a simple formula taking both a pessimistic, most-likely and optimistic estimations into account, providing an improved projection of the project timeline and deliverables.

A critical path is identified and determined within the network diagram, which is the path of tasks the project must complete on time for the entirety of the project to finish on time. Thus, the critical path determines the time duration of the entire complex project. If tasks on the critical path is delayed, the entirety of the project will be behind schedule. The critical path highlights the tasks that focus for the project to become a succus. Mangers using PERT can include a risk management of the individual tasks to identify problem areas and create a plan to deal with the potential of these problems.

PERT visualizes the tasks needed to complete to finish the project. This can greatly help managers to improve communication, planning and scheduling, identify project stakeholders and improve the execution of the project. PERT is an extremely flexible tools which can be tailored to help the project managers with their specific need, for them to best deliver on their goal or project. This article will provide a guide for project managers to implement PERT when tackling complex projects and a thought example of a project where PERT and CPM is applied to estimate the duration.

Big Idea

Project managers are often tasked with generating a projection of the estimated time of a projected to be completed. Complex projects can easily be too complex to comprehend and estimate a realistic timeline. In addition, a proper planning of a complex project is often needed to ensure a high-quality deliverable for the project manager. This is where the tool/method PERT shines and can help the project manager to provide project owners with a realistic timeline, plan, and schedule for the project.

PERT is a method or tool to digest advanced and complex project into smaller, more tangible tasks. The goal of PERT is to use the tasks to better estimate, plan and execute the desires project. By visualizing the decomposed tasks in a network diagram, managers are provided with an overview of the entirety of a project.

Managers in collaboration with their team can use PERT to better estimate the duration of project, to help them deliver on time and risk asses the tasks within the project. Each tasks duration in the network diagram is estimated and a critical path can be established. The critical path in the network diagram is the path through the essential tasks that requires on time completion for the project to complete on time. The duration of tasks in the critical path can summarized to provide the manager with a more realistic estimate of the project.

Tasks durations is estimated through multiple factors. Firstly, an optimistic, most-likely and pessimistic estimation of the singular task is estimated. Secondly, the estimations are then calculated with statistical methods to provide the manager with the best possible time estimation.

Application

When faced with a big/complex project, project managers can benefit from applying PERT. To provide an overview of the method, a sequence of task is listed below for managers to follow when implementing PERT. This description of PERT below is inspired by Jean-Michel Réveillac.

1. Identify tasks
   1. Sequence of tasks with relationships and dependences
   2. Building a network diagram
2. Estimation and calculation of tasks durations
   1. Estimation: Pessimistic, optimistic and most-likely
3. Identification of the critical path
   1. Calculation of estimated project completion time
4. Risk management
   1. Identify potential risks to the project

Identify tasks

When assigned with a complex project, the first step when using PERT is to divide the project into smaller tasks.

Sequence of tasks with relationships and dependences

When tasks have been defined, the sequence of the completion of tasks should be set by the manager. Usually, a number is given to each task or activity. The start tasks are numbered with a 0, to indicate the starting point. No tasks or activity can be a predecessor to task 0. A table of the relationship and dependences of each task, also called predecessors and successors, is setup within a table. Often when applying the sequence table, an additional column describing the activity is included to provide overview for the engaged actors.

It is important that there is only one start and end task