What is PERT? Objectives, Pros & Cons

Program Evaluation And Review Technique (PERT) is a project network analysis technique to plan and control projects by focusing on the time and the cost of each activity involved in the project.

PERT is an approach that helps managers to evaluate and prioritize projects based on the resources available and the expected outcomes. It is used for planning purposes and to determine how much time should be spent on different aspects of a project.

What is PERT? Objectives, Pros & Cons

The PERT technique focuses on the time and the cost taken by each activity. This influences the resultant time and the cost required for the completion of the entire project.

The basic objective of PERT in construction management, its features, pros, and cons are outlined in this article. 

Objectives of PERT Analysis

The main objectives are:
  • A powerful coordinating tool for planning, scheduling, and controlling projects
  • The minimization of total project cost and time
  • Effective utilization of resources and minimization of effective resources
  • Minimization of delays and interruptions during the implementation of the project
PERT is an event-oriented project scheduling technique. This method of networking will not show any kind of interdependency between the events mentioned in the network. Hence, a PERT network represents a combination of events, as shown in Figure-2, 10, 20, etc are events.
Fig.2: A PERT Network; te = estimated time for each event

An event is represented in terms of time and resources that are required for the completion of that event. The PERT network does not have a historic chain as in the case of the Critical path method (CPM).

PERT is more applicable to projects that are new, where most of the events are employed for the first time, or for projects that implement new techniques. Hence, PERT-implemented projects are not repetitive in nature.

The important feature of PERT a project manager must know are:
  1. PERT is a combination of simple statistical methods. This technique at its core is all about management probabilities.
  2. PERT and CPM have some similar characteristics, but their focus is different.
  3. PERT similar to other networking techniques, breaks down the tasks into detailed activities.
  4. After obtaining the activities, a Gantt Chart is created that illustrates the interdependencies of the activities.
  5. In the Chart, each node represents each event connected by arrows. The activities are represented by arrows.
  6. Next, the time estimates are determined- Earliest Time, latest Time, and also slack for each activity.
  7. The PERT hence is an event-oriented project technique
  8. It is the best technique for newly developed projects than repetitive projects

Time Estimates in PERT Network Analysis

The three estimation times used in PERT are:
  1. Optimistic Time Estimate (To)
  2. Most Likely Time (Tm)
  3. Pessimistic Time (Tp)
The three-time estimates are determined for each activity. 

1. Optimistic Time Estimate(To) in PERT

It is the fastest time an activity can be completed. Here the assumption made is that all the resources are available and all the predecessor activities are completed as per the plan.

2. Most Likely Time(Tm) in PERT

If the project managers are demanded only to submit a single time for each activity, then they submit the most likely time.

3. Pessimistic Time(Tp)

This is the maximum time required to finish an activity. For cases when everything goes wrong and gets delayed, this time estimate is considered.

These time estimates may seem simple but are very difficult to prepare and calculate for each event. But their details help to leverage useful information about the expected uncertainties in an activity. The time estimates for PERT analysis can be expressed in days, weeks, or months.

Expected Completion Time (T)  and Possible Variance (V) in PERT

T = (To + 4Tm + Tp )/6

Standard Deviation = (Tp - To)/6

Variance V =  Sqaure of Standar Variation = (Tp-To)2/36

Applications of PERT Network Analysis

  1. Research and Development Project (R and D Projects)
  2. Equipment Maintenance and hauling
  3. Construction Projects (Buildings, bridges, and Dams)
  4. Setting up new industries
  5. Planning and launching new products
  6. Design of plants, machines, and systems
  7. Shifting the manufacturing location to another location
  8. Control of production in large shops
  9. Market penetration programs
  10. The organization of big programs, conferences, etc.
The PERT technique possesses many advantages that facilitate the project team and many disadvantages that have to be taken care of by the project managers. The pros and cons of PERT are mentioned below.

Advantages of PERT

The advantages of PERT are mentioned below:
  1. Planning For Large Projects
  2. Visibility of Critical Path
  3. Analysis of Activities
  4. Coordinating Ability
  5. The What-if -Analysis

1. Planning for Large Projects in PERT

The scheduling of project activities is done easily with the help of the PERT system by the project manager. This technique is more active in large sophisticated project works. As PERT is an event-oriented programming technique, three elements are necessary to define an event. They are:
  • What is the time required to perform the event?
  • What comes after the event?
  • What is coming before the event? The answers to the above question make scheduling easier and clear.

2. Visibility of Critical Path in PERT

The PERT method will show the critical path in a well-defined manner. The critical path is the path with activities that cannot be delayed under any circumstances. Proper knowledge about the stack values with limited conditions of dependencies will help the project manager to bring fast and quality decisions that will favor the project performance.

3. Analysis of Activity in PERT

The activity and the events are analyzed from the PERT networks. These are analyzed independently as well as in combination. This will give a picture of the likely completion of the project and the budget.

4. Coordination in PERT

The various departments of the construction organization will deliver data for the PERT activities. Good integration is developed between all the departments which will help in improving the planning and decision-making capabilities of the project team.

The combination of qualitative and quantitative values from a large amount of data will help in improving the coordination of the project activities. This will also improve communication between various departments of the organization.

5. What-if -Analysis PERT

The possibilities and the various level of uncertainties can be studied from the project activities by properly analyzing the critical path. This type of analysis is called what-if-analysis. For these various sets of permutations and combinations are conducted.

Among them, the most suitable combination is taken into consideration. This set chosen will be the one with minimum cost, economy, and best result. This analysis helps to identify the risk associated with any activities.

Disadvantages of PERT

Various Demerits of PERT are mentioned below:
  1. Time-Focused Method
  2. Subjective Analysis
  3. Inaccuracy due to Prediction
  4. Expensive
  5. Other Issues

1. Time-Focused Method

The method of PERT is a time-oriented method, where the time required to complete the respective activity is of higher importance. Hence the time determination of each activity and its allocation is very much necessary. This is done based on an assumption and within this time the work will be completed. If this is not the case issues will arise.

2. Subjective Analysis in PERT

The activities for a project are identified based on the data available. This is difficult in the case of PERT as these are mostly applied for a project that is newly conducted or those without repetitive nature.

The project dealt with by PERT will be fresh project data that make the collection of information to be subjective in nature. This will bring less accuracy to the time and the estimated time. There are chances to have inaccuracy and bias in the sources of data. This makes it unreliable. As this is not repetitive in nature, there is no sense in bringing the records from past historical data.

3. Prediction Inaccuracy

As there are no past records or assistance to bring an outline for the project, predictions take their role. The overall project may move to total loss if the predictions and the decisions are inaccurate. No trial and error method can be employed.

4. Expensive

As this method is carried out based on predictions overall, they find it too expensive in terms of methods employed, the time consumed, and the resources used.

5. Other Issues

This method is highly labor-intensive in nature. As there are chances of an increase in project activities large and complicated networks are developed as many task dependencies come into existence. If two activities share common resources, this technique won't find very apt for the project.

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