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Difference between PERT and CPM with Comparison Chart

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Difference between PERT and CPM with Comparison Chart
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The nuances of project management - in terms of scheduling, executing, planning, monitoring, controlling, goal attainment, etc. - can be understood with the help of PERT and CPM. These popular network-based techniques of project management showcase the sequence and flow of a variety of activities and events. Program (Project) Management and Review Technique or PERT is helpful for those projects in which the time required for taking care of specific activities is unknown. The projects that are recurring in nature are best handled by Critical Path Method or CPM.

This article will help you know more about these two scheduling methods that can be used for designing networks with the purpose of finding their critical path. To begin with, the differences between PERT and CPM are depicted in the form of a comparative chart below.

PERT vs CPM

Basis of Difference

PERT

CPM

Nature

It is a useful project management tool for planning and controlling the timeline of projects. In PERT, the emphasis is on the start and completion of events and not activities. The activities that occur between events cannot be specified.

It is a significant method for keeping the checks and balances of project costs and timelines effectively. CPM networks are activity based and are represented through arrowed lines while the events are represented with circles. The activities can be linked in logical sequence wherein the time assigned to each activity is carefully associated with its cost.

Orientation

PERT is event-oriented. In simple words, PERT networks are interested in   laying focus upon the start or completion of different events rather than the activities themselves

CPM is activity-oriented and related to the cost rather than time

Type of model

Probabilistic Model: The probabilistic tools of PERT offers several estimates for determining the time of completion of given projects. These probabilistic tools also control all the activities involved for a project to be completed at a lower cost and faster rate

Deterministic Model. The deterministic tools of CPM provide an estimate that relates to the cost/ amount of time available for completing a project

Lay focus on

Time frames for the estimation of project completion are determined on the basis of three estimations in PERT: the most probable, the most unfavorable and the most promising

Trade-off between cost and time. It helps project planners to take decisions with respect to which aspect of certain projects are to be reduced or increased; trade-offs are needed

Process of evolution

PERT evolved in the form of a Research & Development project

CPM evolved as a project based on construction.

Estimation

Three times

One time

Best used for

Estimation of high precision time

Time estimates in reasonable forms

Good for the management of

Activities that are unpredictable

Activities that are predictable

Job type

Takes care of tasks that are of non-repetitive nature

Caters to jobs of a repetitive nature

Non-critical/ critical activities

There is no differentiation in how critical an activity is

The activities are differentiated on the basis of their critical and non-critical attributes

Suitability

PERT is most suitable for R&D related activities

CPM takes care of activities that are non-research based, such as projects dealing with ship building, civil construction, etc.

Concept of Crashing

Crashing concept is not applicable

Crashing concept is applicable

Orientation

PERT is event-oriented

CPM is activity-oriented

Monte Carlo simulations

It contains certain outdated weighting factors for the approximation of schedule variation. Monte Carlo simulations, in comparison, are quite powerful and real-time based if modelled correctly

CPM scheduling processes use deterministic links for connecting tasks. Its techniques represent tasks, durations, dependencies, etc. in a schedule. CPM forms the platform on which PERT/ Monte Carlo simulations can be performed

Consideration for Uncertainty

In a PERT network, due consideration is given to uncertainty

In a CPM network, there is no allowance possible for uncertainties with respect to the duration of time needed for project completion

Duration of activity

In PERT, the duration of activities fails to be very accurate and definite

In CPM, the overall duration of activity can be estimated with quite a fair level of accuracy

Relation of cost and time

Time and cost are not related in any way in PERT. In current times, PERT has been extending its functionality in this direction. Given this, the dividing line between PERT and CPM is fading out gradually

In CPM, the objective pertains to the development of a specific and optimum time cost relation

What is PERT?

PERT in project management refers to a planning tool that is useful for the calculation of the time involved in finishing a project realistically. The full form of PERT is Program Evaluation Review Technique. In PERT, charts serve to be the tools that are mostly used for planning tasks in the course of a project. PERT charts are helpful in scheduling and coordinating team members so that they may accomplish their goals easily.

  • PERT has certain similarities with critical path. Both PERT and critical path are used for visualizing the timelines and tasks that have to be perform for a project.
  • It is possible to create three varied time estimates with PERT while creating a project. These time estimates pertain to the estimation of the shortest possible time that may be taken by each task; the maximum probable time; and the longest time that tasks may take in case things fail to go as per the plan.
  • PERT calculations are performed backwards from any fixed end date as the contractor deadlines cannot be moved in typical ways.

What is CPM?

CPM or Critical Path Method is an essential algorithm in project management. It is mostly used for the purpose of planning, scheduling, coordinating and controlling the different of activities in any given project. In case of CPM, it is assumed that specific activity durations are certain and fixed.

  • CPM is appropriate for computing the latest as well as the earliest possible start times pertaining to each activity.
  • CPM processes are designed to differentiate between the non-critical and critical activities. This is in order to gain the advantages of time reduction and avoid long queue generations.
  • There is an important reason behind the identification of critical activities. In case any specific critical activity is delayed, the entire process will be impacted adversely. To avoid this, project managers opt for the Critical Path Method.
  • In CPM, a list consisting of the activities required for project completion is prepared. This is followed by a computation of the time needed for completing every task. Thereafter, the dependency existing between all the activities has to be determined.
  • The path defined in CPM relates to a sequence of tasks in a network. Out of all the available paths, the one that has the maximum length is the critical path.

Conclusion

Over time, there has been a blurring of the techniques and tools of these two powerful and useful tools of project management. Given this, in most projects, both CPM and PERT are being utilized (in combination) to facilitate the completion of all tasks successfully. The main point of differences between PERT and CPM have been put together in this article. In case you have any further queries then do reach out to us through the Comments section given below. We will be happy to assist you at the earliest.


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