Difference between “Critical Path Method” and “PERT Technique” of Network Analysis are as follows:
There are different forms of network analysis, which may be simple or complex, may be very generalized or may be exclusively designed for specific types of projects. PERT/PEP and CPM are the most widely used techniques used in network analysis.
1. Critical Path Method (CPM):
This technique is used for planning, scheduling, estimating and controlling engineering and construction. This method was used by Du Pont in 1959 to schedule plant maintenance shutdowns during changeovers. The lessons learned through this application, later on, was used to plan building construction and other large construction projects.
The key tool in this technique of planning, scheduling and controlling complex construction jobs is a diagram using arrows to represent specific jobs. Such line diagrams clarify the relationships of every task to every other task, which cannot be explained using bar chart. Critical jobs are those jobs which relate to one another (from start to finish of a project), each depending upon completion of the one before it. Total project time, therefore, is the summation of the time to be taken by critical job.
A simplest form of CPM diagram illustrates the jobs to be performed to finish a project (in order of sequence), timing and costs. Once all these elements are specified, both the total time and the total cost of the project can be determined by adding the different sub-elements.
The consequence of various managerial decisions can be predicted by simulating their impact.
2. PERT/PEP Technique:
The PERT/PEP technique is based on critical-path scheduling. However, there is a fundamental difference between PERT/PEP and critical-path scheduling. The PERT/PEP technique is applicable where there is no established system for doing the task and, therefore, no exact basis for estimating the required time to complete each task.
Critical path scheduling, on the other hand, usually is applied to jobs which are established or have been done before and where it is possible to predict performance accurately. Consequently, more sophisticated mathematical models must be used in the PERT/PEP technique.
PERT may, therefore, be defined as follows:
PERT is a statistical technique diagnostic and prognostic for quantifying knowledge about uncertainties faced in completing intellectual and physical activities essential for timely achievement of programme deadlines. It is a technique for focusing management attention on danger signals that require remedial decisions, and on areas of effort for which trade-offs in time, resources or technical performance, might improve capability to meet major deadlines.
The PERT technique is, therefore, based on the concept that in any programme, there are three variables:
(b) Resources (HR, facilities, funds)
(c) Performance specifications
Any one of these may vary within certain limits established for such programme, while holding the other two constant. To take an example, holding time and performance constant, the requirements for resources may be determined.
It is, therefore, clear that both PERT and CPM have similarities in terms of concepts and methodology. We use these techniques in project scheduling problems. However, we use PERT in analysing project scheduling, where completion time is not certain and CPM, where activity durations are known with certainty.
In essence, therefore, PERT is probabilistic in nature and more appropriately used in R&D projects, whereas, CPM is a deterministic technique and thus finds application more appropriately in the construction projects.