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Difference between CPM and PERT

09 Apr 2019 11:09 am || 0

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.

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

PERT and CPM

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 the Critical Path Method or CPM.

Difference between CPM and PERT with the comparison chart

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 a 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 based on three estimations in PERT: the most probable, the most unfavorable and the most promising A trade-off between cost and time. It helps project planners to make decisions to which aspect of specific 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 developed as a project based on construction.
Estimation Three times One time
Best used for Estimation of high precision time Time estimates in reasonable forms
Suitable for the management of Unpredictable activities Predictable activities
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 significant activity is The activities are differentiated based on their vital 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 shipbuilding, civil construction, etc.
Concept of Crashing Crashing idea 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 robust and real-time based if modeled 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 risks 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 period of action can be estimated with quite a fair level of accuracy
Relation of cost and time Time and price 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 quickly.

  • PERT has certain similarities with the critical path. Both PERT and critical path are used for visualizing the timelines and tasks that have to be performed 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 backward 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 planning, scheduling, coordinating, and controlling the different activities in any given project. In the case of CPM, it is assumed that specific activity durations are defined and fixed.

  • CPM is appropriate for computing the latest as well as the earliest possible start times of each activity.
  • CPM processes are designed to differentiate between non-critical and critical activities. This is to gain the advantages of time reduction and avoid long queue generations.
  • There is an essential reason for the identification of critical activities. In case any specific significant action 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. After that, 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 possible ways, 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 for 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.