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 time needed to complete different activities are not known.
On the other hand, Critical Path Method or CPM, is apt for the projects which are recurring in nature.
The two scheduling methods, uses common approach for designing the network and for ascertaing 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 former concentrates on time while the latter stresses on 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.
Content: PERT Vs CPM
|Basis for Comparison||PERT||CPM|
|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.|
|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, organising, coordinating and controlling of 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 1950’s, 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 are 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 behind 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.
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 of uncertain activities is done. CPM is a statistical technique of project management in which planning, scheduling, organising, coordination and control of well-defined activities takes 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 research and development project, CPM evolved as construction project.
- PERT is set according to events while CPM is aligned towards activities.
- A deterministic model is used in CPM. Conversely, PERT uses 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 least additional cost. The crashing concept is not applicable to PERT.
The difference between these two project management tools is getting blurred as the techniques are merged with the passage of time. That is why, in most projects, they are being used as a single project. The primary point that distinguishes PERT from CPM is that the former gives the extreme importance of time, i.e. if the time is minimised, consequently the cost will also be reduced. However, cost optimisation is the basic element, in the latter.