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Pert and CPM

Project management can be understood as a systematic way of planning, scheduling, executing, monitoring, controlling the different aspects of the project, so as to attain the goal made at the time of project formulation. PERT and CPM are the two network-based project management techniques, which exhibit the flow and sequence of the activities and events. Program (Project) Management and Review Technique (PERT) is appropriate for the projects where the time needed to complete different activities are not known.

On the other hand, the Critical Path Method or CPM is apt for the projects which are recurring in nature.

The two scheduling methods use a common approach for designing the network and for ascertaining its critical path. They are used in the successful completion of a project and hence used in conjunction with each other. Nevertheless, the truth is that CPM is different from PERT in a way that the latter concentrates on time while the former stresses on the time-cost trade-off. In the same manner, there are many differences between PERT and CPM, which we are going to discuss in this article.

Comparison Chart

Meaning PERT is a project management technique, used to manage uncertain activities of a project. CPM is a statistical technique of project management that manages well defined activities of a project.
What is it? A technique of planning and control of time. A method to control cost and time.
Orientation Event-oriented Activity-oriented
Evolution Evolved as Research & Development project Evolved as Construction project
Model Probabilistic Model Deterministic Model
Focuses on Time Time-cost trade-off
Estimates Three time estimates One time estimate
Appropriate for High precision time estimate Reasonable time estimate
Management of Unpredictable Activities Predictable activities
Nature of jobs Non-repetitive nature Repetitive nature
Critical and Non-critical activities No differentiation Differentiated
Suitable for Research and Development Project Non-research projects like civil construction, ship building etc.
Crashing concept Not Applicable Applicable

Definition of PERT

PERT is an acronym for Program (Project) Evaluation and Review Technique, in which planning, scheduling, organizing, coordinating and controlling uncertain activities take place. The technique studies and represents the tasks undertaken to complete a project, to identify the least time for completing a task and the minimum time required to complete the whole project. It was developed in the late 1950s. It is aimed to reduce the time and cost of the project.

PERT uses time as a variable which represents the planned resource application along with performance specification. In this technique, first of all, the project is divided into activities and events. After that proper sequence is ascertained, and a network is constructed. After that time needed in each activity is calculated and the critical path (longest path connecting all the events) is determined.

Definition of CPM

Developed in the late 1950s, Critical Path Method or CPM is an algorithm used for planning, scheduling, coordination and control of activities in a project. Here, it is assumed that the activity duration is fixed and certain. CPM is used to compute the earliest and latest possible start time for each activity.

The process differentiates the critical and non-critical activities to reduce the time and avoid the queue generation in the process. The reason for the identification of critical activities is that, if any activity is delayed, it will cause the whole process to suffer. That is why it is named as Critical Path Method.

In this method, first of all, a list is prepared consisting of all the activities needed to complete a project, followed by the computation of time required to complete each activity. After that, the dependency between the activities is determined. Here, ‘path’ is defined as a sequence of activities in a network. The critical path is the path with the highest length.

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Key Differences Between PERT and CPM

The most important differences between PERT and CPM are provided below:

  • PERT is a project management technique, whereby planning, scheduling, organising, coordinating and controlling uncertain activities are done. CPM is a statistical technique of project management in which planning, scheduling, organising, coordination and control of well-defined activities take place.
  • PERT is a technique of planning and control of time. Unlike CPM, which is a method to control costs and time.
  • While PERT is evolved as a research and development project, CPM evolved as a construction project.
  • PERT is set according to events while CPM is aligned towards activities.
  • A deterministic model is used in CPM. Conversely, PERT uses a probabilistic model.
  • There are three times estimates in PERT, i.e. optimistic time (to), most likely time ™, pessimistic time (tp). On the other hand, there is only one estimate in CPM.
  • PERT technique is best suited for a high precision time estimate, whereas CPM is appropriate for a reasonable time estimate.
  • PERT deals with unpredictable activities, but CPM deals with predictable activities.
  • PERT is used where the nature of the job is non-repetitive. In contrast to, CPM involves the job of repetitive nature.
  • There is a demarcation between critical and non-critical activities in CPM, which is not in the case of PERT.
  • PERT is best for research and development projects, but CPM is for non-research projects like construction projects.
  • Crashing is a compression technique applied to CPM, to shorten the project duration, along with the least additional cost. The crashing concept is not applicable to PERT.

Public Administration by G.Rajput


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