PERT Estimation Technique

PERT (Program Evaluation Review Technique) is an estimation technique that was first developed and applied by the United States Defence establishment for their Ballistic Missile development program. It was one of their most ambitious programs. Completion of this in time ahead of the other nations was critical for them. Such a missile development program was filled with a huge amount of uncertainty, as it required a large number of supplier agencies working on new technology development. This method of estimation helped them build in all the uncertainties in their estimates and helped them to complete this program ahead of their expected schedule.

PERT Formula 

The PERT estimation technique (Program Evaluation Review Technique) formula is a cornerstone of the three-point estimation method, designed to handle the uncertainties inherent in project tasks. It uses three types of estimates: 

O (Optimistic Estimate): The shortest possible time required to complete the task, assuming everything proceeds better than is typically expected. 

M (Most Likely Estimate): The best estimate of the duration required to complete the task, assuming everything goes as normal. 

P (Pessimistic Estimate): The logest time that might be taken to complete the task, assuming everything goes wrong.  

The formula to calculate the Expected Time (TE) is: 

TE= (O+4*M+P)/6

This formula not only calculates an average of the estimates but gives the most weight to the most likely outcome, making it a robust tool for project managers.  

PERT Example 

Consider a project task of designing a website. The optimistic time to complete the design is 10 days, the most likely time is 15 days, and the pessimistic time is 25 days. Using the PERT formula, the expected time (TE) would be calculated as follows:

TE= (10+4*15+25)/6=(10+60+25)/6=95/6≈15.83

The Three Chances 

The three estimates in PERT represent the three chances or scenarios under which a project might unfold: 

• 1.TOPT (Optimistic Scenario) or O: This TOPT scenario envisions a case where everything goes right, typically the least likely scenario but important for establishing a best-case timeline. 
• 2.TLIKELY (Most Likely Scenario) or M: This TLIKELY scenario is the scenario that is believed to be the most realistic and probable, based on past experiences and typical conditions. 
• 3.TPESS (Pessimistic Scenario) or P: This TPESS scenario accounts for the worst-case scenario, considering potential setbacks and challenges that could delay project completion. 

PERT Estimation Process 

The PERT estimation technique involves several key steps: 

• Identify Tasks: This step involves listing all tasks required for the project. 
• Estimate Times: Now, we need to assign optimistic, pessimistic, and most likely times for each task to take place. 
• Apply PERT Formula: We now would need to use the PERT formula discussed in the earlier section to calculate the expected times for all tasks. 
• Analyze and Adjust: We now would need to review the calculated times for feasibility and realism, and adjust estimates and plans accordingly. 
• Monitor and Update: Continuous monitoring of actual task durations and update estimates and plans as needed to reflect real-world conditions is to be done as part of this process step. 

Benefits of Using PERT Estimation 

Using PERT estimation technique offers several benefits: 

• Improved Accuracy: By considering different scenarios, the PERT technique provides a more realistic view of potential outcomes. 
• Risk Management: This estimation technique helps in identifying potential risks by analyzing the variance between optimistic and pessimistic scenarios. 
• Better Planning: PERT technique supports effective planning and scheduling by providing a balanced outlook on project timelines. 

 Pros and Cons of PERT 

Pros: 

• The PERT approach facilitates contingency planning and risk assessment. 
• It reduces uncertainty and increases reliability of project timelines. 
• And also, this enhances communication and planning through clear, quantified timelines. 

Cons: 

• PERT can be time-consuming to gather three accurate estimates for every task. 
• This relies on subjective estimates, which can vary significantly among project team members. 
• It may not be as effective for projects where tasks are not clearly definable or are highly novel. 

PERT Common Pitfalls and How to Avoid Them 

Pitfalls: 

• Over-reliance on Historical Data: Using outdated or irrelevant data can skew PERT calculations leading to improper project planning. 
• Subjectivity in Estimates: Different team members may have varied perceptions of optimistic and pessimistic scenarios. 

Avoidance Strategies: 

• We need to regularly update and validate data sources to ensure relevance and accuracy. 
• We can facilitate consensus-building sessions among stakeholders to align team perceptions and understandings of task complexities. 

By understanding and applying these elements of PERT, project managers can enhance their planning effectiveness and increase the likelihood of project success. 

Conclusion

PERT estimation technique will be a practical approach for estimating when the tasks on hand are filled with uncertainties, where the tasks may take up different estimates depending upon certain conditions. Project management professional certification is a perfect way to learn this technique while preparing. The actual estimate is dependent on certain variables. PERT allows the preparation of a more practical estimate by factoring the 3-point estimates into one as explained above.