Programme Evaluation and Review Technique
Complex projects require a series of activities, some of which must be performed sequentially and others that can be performed in parallel with other activities. This collection of series and parallel tasks can be modeled as Network. The most common network technique used for this purpose is programme evaluation and review technique abbreviated as PERT which uses graphical representation of a project .PERT was developed by Naval Engineers of USA Navy , in charge of Polaris Sub-Marine Missile project in 1958 for the use in planning and scheduling of the construction of marines and missile control. When the activity time is probablistic, PERT can be used. In this method, threee times estimates are made for each activity and these are used to compute expected project completion time and its variance. PERT was strictly oriented to the time element of project and used probabilistic activity time estimates to aid in determining the probabilty that a project could be completed by some given date.
Concept of programme evaluation and review technique
The concept of programme evaluation and review technique works on three times estimate of activity of a project. The concept of three time estimate was evolved to reduce th extent of uncertainity. The above mentioned three time estimate suggests :
1.Optimistic time (a) – This indicates the minimum time an activity can take if everything goes smoothly without any interruptions. The optimistic time is representated by ‘a’.
2. Pessimistic time (b) – This indicates the longest time that an activity might require if everything goes wrong in a sort of catastrophe. Pessimistic time is denoted by ‘b’.
3. Most likey time (m) – The completion time having the highest probabilty . it is signified as ‘m’.
Three time estimates are not directly entered into network. They are transfomed into an expected time ,te, using the statistical relation : te = a + 4m + b / 6
Steps for programme evaluation and review technique analysis
1. Identify Activities and Milestones.
2. Determining Activity Sequence.
3. Construct the Network Diagram (AOA Basis)
4. Estimate Activity Times.
5. Determine the critical path.
6. Update PERT chart as Project Progresses.
Benefits of PERT
1. It reveals the interdependencies and problem areas, which are well defined by conventional methods.
2. It keeps the management alert by computing and checking the variations.
3. It is an effective mechanism for planning, scheduling and co-ordinating the different activities in project.
4. Scheduled Activity start and end dates.
5. It enables the optimum utilisation of resources and there is a probablity of completion before specified date.
1. Because other paths can become the critical path if their associated activities are delayed, PERT underestimates the
expected project completion time.
2. The activity time estimates are somewhat subjective and depend on judgement.