Difference Between PERT and CPM

Difference Between PERT and CPM

CPM stands as Critical Path Method whereas PERT stands as a Project/Programme Evaluation and Review Techniques. CPM/PERT can be described as a pictorial representation of inter-relationship and sequence of all the required construction activities which constitute the Project.
                                                                                        CPM and PERT are regarded as very powerful numerical tools off project management and they facilitate the work of planning, organizing, scheduling, controlling, monitoring and evaluating the project in the most effective way. difference between CPM and PERT are as follows:

Difference Between PERT and CPM

What is PERT?

PERT or Programme Evaluation and Review Technique is a management tool used for planning, controlling and reviewing a project. It was developed by the U.S. Navy along with a management consultancy firm for its Polaris Missile Program.
                 An important characteristic of any project is its duration. The effectiveness and economy of the project are often dependent on the project duration. The total project duration depends on the time taken for each event to occur. to estimate the time required for each event to occur, it requires the planner to have a wide experience, with similar.

                                     The estimate of the time duration can be done in two ways. one is the deterministic approach in which the planner with enough knowledge about the project gives a single estimate of the duration which is sufficiently accurate. The other approach is a probabilistic approach in which accurate information is available, hence only the limits within which the duration will lie, is estimated.

               PERT follows this second approach or the probabilistic approach towards time durations. Pert is also an event-oriented network method where more importance is given to the achievement of a discernible milestone rather than the activity itself.

                   Because of these characteristic PERT was developed and has been used in R and D type projects such as space industry, defence industry etc. Such projects are of a non-repetitive type or once-through type in which correct time estimate cannot be made.

What is CPM?

The CPM or Critical Path Method was discovered jointly by Dupont and Remington Rand Univac in 1957. This research team was trying to determine how best to reduce the time required to perform routine plant overhaul, maintenance and construction work. Since the CPM is found to be of much use in the construction industry with applications in the construction of massive structure like bridges, dams, tunnels, high-rise building etc.

                                                        CPM networks are usually used for the repetitive type of project, where fairly accurate estimates of time can be made for the activities of the project. The activities of these project are characteristically subject to a relatively small amount of variation. That’s why CPM is not suitable for research and development type of projects.

Difference Between PERT and CPM

It is basically having a DETERMINISTIC approach in the design of network.
It is basically having PROBABILISTIC approach in the design of network.
The only a one-time estimate is required for each activity.
Three-time estimate (in the form of Pessimistic time, Optimistic time and Most likely time) for each activity.
It is built-up of an activity-oriented diagram.
It is built-up of an event-oriented diagram.
Time and cost both are controlling factors. There is an optimum duration of the project at which the project cost is minimum and this can be obtained by cashing the network.
Time only is the controlling factor and the cost is assumed proportional to the project duration.
Critical events must have zero.
Critical events may be positive/negative depending upon the project scheduled completion time.
It is recommended for the repetitive nature of work where past experience are adequately available.
It is recommended for research and development project where no past experiences are available or where great uncertainty lies in the time estimation.

                                                           PERT is the general case where the activity time is described by three times estimates, measure the uncertainty by standard deviation and variance, whereas the CPM is the particular case when all the three-time estimate coincide with one value ( called deterministic time) and the standard deviation and variance disappear.

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