Project Evaluation and Review Technique (PERT)

A project consists of a large number of activities, scheduling of which by the conventional method of generally difficult. In case, the projects are not properly scheduled, they tend to extend beyond the expected date and cause heavy losses to the organization (firm).

The following important points should be considered before starting scheduling of any projects:

·       The contracting firms shall be able to meet the commitments, if there is proper scheduling.

·        A firm can face competition if there is proper scheduling.

·      Scientific scheduling of a project is an important factor, particularly for the firm engaged in turn key projects.

·     Scheduling of a project can be performed through Critical Path Analysis (CPA).

·    Critical Path Analysis is an important device for the scheduling of a job. It is a synthesis of two independent techniques viz. Program Evaluation and Review Technique (PERT) and Critical Path Method.

·      PERT was first developed by the Naval Engineers of USA and the Navy incharge of the Polaris Missile Project.

·       Both are methods viz. CPM and PERT are only superficially different; they have many things in common and they are combined into a technique called Critical Path Analysis (CPA).

·  CPM is an activity-oriented technique, while PERT is an event-oriented technique. An event means the beginning or the ending of one or more activities. The PERT network diagram uses the line and arrow to conceptualize the events (shows by circles o) which are related to each other.

·        CPM has one time estimate, while PERT has three different time estimates.

The relation between an event and an activity

·        PERT uses three time estimates.

§  Optimistic time (a)

§  Most likely time (m)

§  Pessimistic time (b)

§  Optimistic Time

In the case of optimistic time, it is presumed that everything will work according to the estimation of minimum possible time. An activity takes place in ideal conditions. No problem is made for any delay. This estimated time is denoted by ‘a’.

§  Most Likely Time

In this case, activities take place in a normal way, with a few delays and setbacks here and there. The most likely time lies between the optimistic time and it is denoted by ‘m’.

§  Pessimistic Time

In this case, the time is based on the presumption that everything will run badly. It is the max = mum possible time taken into consideration for the completion of an activity. But it does not, however, include such unforeseen events like labour strikes, natural calamities etc. This time factor is denoted by ‘b’.

§  Expected Time or Average

According to distribution we can get the expected time (t) by adding together 1/6^th of the optimistic time, 2/3^rd of the most likely time and 1/6^th of the pessimistic time estimates.

 t_e  (expected time) = 1/6 a + 2/3 m + 1/6 b

OR

 t_e  =  a + 4m + b / 6

performances of these activities depend upon several factors like equipment, personnel problems etc. To keep the schedule, additional resources are provided for facing difficulties, if they arise in any of the activities.

The equation is important for PERT analysis. The expected time shows that there are equal chances of getting the job done within that time limit.