CPM VS. PERT

CPM stands for Critical Path Method and PERT stands for Program Evaluation and Review Technique. These are network techniques used to aid in the planning, scheduling, monitoring, and control of activities which are related to each other. CPM is frequently used in the construction industry to help organize and schedule those activities which together constitute a given construction project. PERT was first used to help coordinate the activities in the development of the Polaris missile system.CPM and PERT are two powerful tools for faster and more efficient completion of complex projects. Both methods show precedence relationships explicitly. Although the two methods were developed independently during the fifties, they are surprisingly similar. Both methods, PERT and CPM, use a graphic representation of a project that it is called "Project Network" or "CPM diagram", and it is used to portray graphically the interrelationships of the elements of a project and to show the order in which the activities must be performed.

PERT

There is high degree of uncertainty pertaining to completion time of certain activities. Particularly in research and development projects, it is difficult to gauge the time the project will take to complete. In such cases we can take probabilistic approach for each activity and define optimistic time estimate, most likely time estimate and pessimistic time estimate. With expected time for each activity, it is possible to determine the critical path. Thus PERT is a probabilistic tool that makes use of 3 estimates for completion of activities and is a tool for planning and control of time for completion of a project.

  Another derivative of the GANTT chart

  Multiple time estimates were used for each activity that allowed for variation in activity times

  Activity times are assumed to be random, with assumed probability distribution ("probabilistic")

  Activities are represented by arrowed lines between the nodes or circles

CPM

CPM on the other hand is a deterministic tool taking only a single estimate of time for completion of any activity in a project. It also allows for estimate of costs, thereby being a tool that can control both time as well as costs.

• Tool to analyze project and determine duration, based on    identification of "critical path" through an activity network.
• Knowledge of the critical path can permit management of the project to change duration.
• A single estimate for activity time was used that did not allow for variation in activity times
• Activity times are assumed to be known or predictable ("deterministic")
• Activities are represented as nodes or circles

PERT(Program Evaluation and Review Technique)	CPM (Critical Path Method)
1) PERT is a probabilistic tool used with three estimating the duration for completion of estimate of duration.	1) CPM is a deterministic tool, with only single activities.
2) This tool is basically a tool for planning and control of time.	2) CPM also allows and explicit estimate of costs in addition to time, therefore CPM can control both time and cost.
3) In routine projects where estimated time for each activity is known, CPM is a better tool to control both time and cost than PERT.	3) In routine projects where estimated time for each activity is known, CPM is a better tool to control both time and cost.
4) The probability factor i major in PERT so outcomes may not be exact.	4) The deterministic factor is more so values or outcomes are generally accurate and realistic.
5) Where the estimation of time for each activity is difficult such as R&D, PERT is a more suitable method	5) Where the estimation of time for each activity is difficult such as R&D, CPM is a not suitable method