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PERT (Program Evaluation Review Technique) is an estimation technique which was first developed and applied by 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 missile development program was filled with huge amount of uncertainty, as it required large number supplier agencies working on new technology development. This method of estimation which helped them build-in all the uncertainties in their estimates and helped them to complete this program ahead of their expected schedule.PERT uses a three point estimation approach for a task. Any task filled with uncertainties can have a wide range of estimate in which the task actually will get completed. Uncertainties include both favourable conditions (opportunities) as well as unfavourable conditions (threats). PERT includes statistical analysis.The 3 points of estimates are as below:Optimistic estimate – Estimate when all favourable things will happen (all opportunities happen and no threats take place)Pessimistic estimate – Estimate when all unfavourable conditions happen (all threats happen and no opportunities take place)Most Likely estimate – Estimate when both favourable and unfavourable conditions will happenFor example, if we think about a task which involves travelling in a crowded city from a specific location in the city to the airport. Actual time taken will depend upon the traffic condition on the road. This may take optimistically 30 minutes, pessimistically 90 minutes and most likely 60 minutes. So the range in which the travel time will fall is 30 minutes to 90 minutes. An average expected estimate is calculated by taking a weighted average of these 3 points of estimates using below formula:E (Mean PERT Average) = (O+4ML+P)/6   (by giving more weightage to most likely estimate)Standard Deviation (SD) = (P-O)/6Actual time taken to travel will be anything within this range with the most likely duration as 60 minutes. PERT allows applying statistical concepts to study the probabilities of completing the tasks in a particular estimate range. Assuming that the mean is exactly in the middle, and assuming the actual estimates will follow a normal distribution within the extreme range of optimistic and pessimistic estimates, we can predict the following probabilities of completing the task in certain range of time as below:Mean +/- 1 Standard Deviation range – Probability is 68.4%Mean +/- 2 Standard Deviation range – Probability is 95.5%Mean +/- 3 Standard Deviation range – Probability is 99.7% ConclusionPERT 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. Actual estimate is dependent on certain variables. PERT allows preparing a more practical estimate by factoring the 3 point estimates into one as explained above. 
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Project Management Tutorial

PERT Estimation Technique

PERT (Program Evaluation Review Technique) is an estimation technique which was first developed and applied by 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 missile development program was filled with huge amount of uncertainty, as it required large number supplier agencies working on new technology development. This method of estimation which helped them build-in all the uncertainties in their estimates and helped them to complete this program ahead of their expected schedule.

PERT uses a three point estimation approach for a task. Any task filled with uncertainties can have a wide range of estimate in which the task actually will get completed. Uncertainties include both favourable conditions (opportunities) as well as unfavourable conditions (threats). 

PERT includes statistical analysis.

The 3 points of estimates are as below:

  • Optimistic estimate – Estimate when all favourable things will happen (all opportunities happen and no threats take place)
  • Pessimistic estimate – Estimate when all unfavourable conditions happen (all threats happen and no opportunities take place)
  • Most Likely estimate – Estimate when both favourable and unfavourable conditions will happen

For example, if we think about a task which involves travelling in a crowded city from a specific location in the city to the airport. Actual time taken will depend upon the traffic condition on the road. 

This may take optimistically 30 minutes, pessimistically 90 minutes and most likely 60 minutes. So the range in which the travel time will fall is 30 minutes to 90 minutes. 

An average expected estimate is calculated by taking a weighted average of these 3 points of estimates using below formula:

  • E (Mean PERT Average) = (O+4ML+P)/6   (by giving more weightage to most likely estimate)
  • Standard Deviation (SD) = (P-O)/6

Actual time taken to travel will be anything within this range with the most likely duration as 60 minutes. PERT allows applying statistical concepts to study the probabilities of completing the tasks in a particular estimate range.

 Assuming that the mean is exactly in the middle, and assuming the actual estimates will follow a normal distribution within the extreme range of optimistic and pessimistic estimates, we can predict the following probabilities of completing the task in certain range of time as below:

  • Mean +/- 1 Standard Deviation range – Probability is 68.4%
  • Mean +/- 2 Standard Deviation range – Probability is 95.5%
  • Mean +/- 3 Standard Deviation range – Probability is 99.7% 

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. Actual estimate is dependent on certain variables. PERT allows preparing a more practical estimate by factoring the 3 point estimates into one as explained above. 

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Comments

Prakruthi

In these project management tutorials, I have learned the Techniques & methodologies and in this article, anyone can learn the basics of PMP to latest and advanced levels of PMP. I have referred some other website but no website provided this much detailed information about project management really thanks for the website for guiding the professionals to be good at our project management carriers.

Clife

Clear and understandable notes

Muwanguzi Edward

Good information to enhance good communication

Ali

Thanks .the information you provide is very important

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