Published on August 18, 2019
Updated on June 25, 2020
Read time 11 minutes
PERT Guide For Project Managers and Productivity Gurus
Since we preach so much about project management and productivity, there aren’t a lot of case studies going on. The weird thing is that this phenomenon is common all over at different productivity blogs. However, we decided to dedicate this weak to the Project Evaluation and Review Technique (PERT) study guide. The following write-up is not a detailed analysis, but it is more than enough to give you a gist of what PERT is.
If you are a project manager who is just about getting started in the industry, our PERT study guide will help you to avoid the pitfalls, which usually the new ones fall in. In addition, there are some dos and don’ts of PERT methodologies that we deem essential to project management for all sorts of managers.
PERT or Project Evaluation and Review Technique is a statistical tool that is used in project management to estimating the minimum time required for a project to complete by analyzing all the tasks required and by calculating the minimum time it would take to complete each task in the project.
The PERT chart is a crucial part of PERT methodology as it shows how to schedule, organize and coordinate tasks during a project. PERT Methodology allows the project manager to devise a budget depending upon the duration of the project without knowing all the details and durations of the tasks and to closely monitor the progress of the project. This methodology is favorable for projects where time is a bigger concern than cost, thus this methodology is a popular event-oriented technique.
This technique was devised by the U.S. Navy’s Special Projects Office in cooperation with the management consulting firm of Booz, Allen, and Hamilton when developing the Polaris submarine missile program in 1957. Thus, the technique is most suitable for large-scale, one-time, complex, non-routine infrastructure and Research and Development projects.
The 1968 Winter Olympics in Grenoble is an early example of the usage of the PERT technique. PERT was used from 1965 till the opening of the 1968 Games.
PERT is often mentioned in conjunction with the Critical Path Method (CPM), a similar statistical method for forecasting progress which was developed by project management personnel in the private sector around the same time as PERT.
Although there are strong similarities between both techniques, they are complementary tools and are often referred jointly as PERT/CPM technique.
Source: Blair Singer
The PERT Technique
The PERT Technique starts by understanding all the tasks required for the project to complete and how much time it would take each activity to complete. The time for each task is calculated by estimating three durations: Optimistic, Realistic and Pessimistic. The duration estimates range from the best case to the worst case and assume that these estimates are accurate. The weighted average is used to calculate the time estimate for each task. This method ensures that the probability of the time duration of each task taking more time than estimated has been minimized.
With the PERT Analysis, the expected entire project duration and the probability with which the specific deadline can be reached is calculated. It also helps in calculating the expected critical path on the expected duration of each activity.
Source – Projectmanager.com
Once the estimated time for each activity has been calculated the PERT chart can be drawn. The graph illustrates the project as a network diagram consisting of numbered, sequential nodes that represent events or milestones linked together vectors that represent tasks in the project. The critical path of the entire project is calculated by estimating the longest time it would take for all the tasks to complete without any slack.
The PERT Chart helps identify tasks that are concurrent and dependent and gives a visual representation of how long it will take each task to complete. This helps the project manager allocate resources efficiently. For example, Task I cannot begin before Tasks A to H is all completed. However, the resources that were working on Task H would be finished a day before Task I can begin. The project manager will easily see this and allocate these freed up resources to work on something else.
Steps in the PERT Planning Process
1. Identifying Activities and Milestones
Tasks and milestones are often written listed in a table in which information like sequence and duration is later added.
2. Determining Activity Sequence
This is a straight forward process for most project managers and allows them to efficiently employ project resources.
3. Construction of the Network Diagram
For complex and large projects, this phase is made easier by dividing the tasks into subtasks. This also makes it easier to manage large teams.
4. Estimation of Activity Times and Probabilities
PERT is used to deal with uncertainty related to activity completion times.
Critique of the PERT Methodology
Benefits of the PERT Methodology
PERT is an ideal methodology for large and complex projects as it
- Estimates the expected project completion time.
- Estimates the probability of completion before a specified date.
- Identifies the activities/tasks that directly impact the completion time (Critical path).
- Pinpoints when parallel activities can be performed.
- Explicitly define and make visible dependencies.
- Appraises the sequence of activities/tasks as well as the scheduling and timings of the activities/tasks.
- Identifies the activities/tasks that have slack time and from where resources can be acquired to aid activities/tasks on the critical path.
- Estimates the project and activities/tasks start and end dates.
- Depicts the data and information in an organized manner.
- Aids in decision-making.
- Potentially reduces project duration due to a better understanding of dependencies.
Limitations of the PERT Methodology
Like any technique, PERT is not without its limitations. Some of its limitations are as follows:
- The time estimates are subjective and may prove to be biased.
- PERT ignores all paths other than the critical path. This can become problematic when other paths become critical paths when one or more activity/task is delayed. This may cause the project to be delayed.
- For very large and complex projects there may be thousands of tasks and individual dependency relationships.
- PERT is not easily scalable for smaller projects.
- For many projects, the network charts can be large and unwieldy.
Time is the only variable. The effects of resource and technical performance changes enter into the analysis only regarding their effect on elapsed time for the affected activity (Monte Carlo has a similar limitation).
- Only One Distribution
The potential range of outcomes for any activity can vary depending on the type of work contained in the activity. PERT is limited to the single ‘Modified Beta’ distribution, modern systems allow a range of different distributions to more accurately reflect the variability inherent in each activity.
- Modern tools use:
Triangular, Normal (Gaussian), Beta, Flat (no preference for any value between the max & min) and customizable distributions to name a few. This limitation in PERT reduces the accuracy of the calculation. The Calculation for SD is an Approximation. The PERT calculation for the value of the SD is a significant source of error. Modern computers can easily manage the more complex calculations needed to accurately assess the actual SD for a data set.
- The Single Pass Calculation
The single-pass PERT calculation generates a single value. Techniques such as Monte Carlo run many hundreds of simulations that generate significantly richer and more accurate information.
- The PERT Merge Bias
The single-pass PERT calculation based on the ‘critical path’ ignores the possibility that other sub-critical paths may take longer to complete under certain circumstances. In the sketch above, if the critical path is achieving an outcome close to its ‘most likely’ date, but the sub-critical path is heading towards a pessimistic outcome, the project completion will be delayed, but the PERT calculations fail to recognize this.
Real-Life Applications of the PERT Methodology
The adaptability of PERT means that it can be implemented for many projects. PERT can be used for a variety of projects, including the following types.
- Research and development of a new product
- NASA space exploration projects
- Movie productions
- Educational planning and development
- Planning and organizing sporting events
- Government-sponsored projects for developing a new weapons system
- Maintenance of a nuclear reactor
- Installation of a management information system
Applications of the PERT Methodology
PERT can be adapted and used for a variety of projects. However, by its very nature, PERT is used for projects where estimating the time required for each task and the whole project involves some uncertainty.
U.S. Navy’s Polaris missile development program
Background and Problem
The development of PERT was born out of sheer necessity. In 1956, the U.S. Navy’s Special Projects Office was working on the Polaris missile development program. Concerned with the Soviet Union’s growing nuclear arsenal, U.S. Navy wanted to speed up the process, however, they discovered that all the conventional management methods were inadequate for handling such an immense project.
U.S. Navy’s Special Projects Office helped by the Lockheed Missile Systems division and the Consultant firm of Booz-Allen & Hamilton devised PERT to address the issues faced by the Polaris missile development program. The solution was devised keeping in view the uncertainty involved in coordinating the efforts of 11,000 contractors. The methodology was developed keeping in view time as the critical factor.
The calculations were so arranged so that they could be carried out on the IBM Naval Ordinance Research Computer (NORC) at Dahlgren, Virginia. The methodology was so successful that it is attributed to the completion of the projects two years before the original estimate. The success of this application led the U.S. Department of Defense to specify that all future defense contracts must use PERT.
Persian Gulf War
Background and Problem
In 1991, the Persian Gulf War is well underway. General Schwarzkopf directed that the logistics community keep a 60-day supply of material on hand which included medical supplies, fuel, etc. Conservative medical supplies estimates alone amounted to 26,352 short tons. The combat unit was designed for mobility and survivability and thus carried only two-day supplies on missions. They relied heavily on a steady source of new supplies.
Using PERT, resupply technique was optimized in such a way that the optimized the resupply time from 6 hours to 3 hours and allows both the supply team combat unit to be on the move during resupply activity. This helped increase security, and supply vehicles make more round trips in the same amount of time. This also gave greater freedom to the tactical commander in planning as less time was taken up by resupply activities.
Laboratory Research and Development Planning-Temperature Study
- Research team
- Hospital management
- Hospital Staff
- Technical Consultants
- Pilot study followed by a clinical study
- Transcutaneous pc02 monitoring was clinically desirable for premature infants
- Study complex temperature and clinical studies in a neonatal intensive care unit patient population
- Development of new equipment and electrodes
- Design of an electrode buffer solution with a fast time response
- Complex temperature and clinical studies in a neonatal intensive care unit patient population
Ø Select premature infant for study
Ø Get consent from parents to participate in the study
Ø Take temperature
Ø Record temperature
Ø Parents volunteer themselves
Ø No premature birth
Ø Problem taking the temperature
Ø Time Crunch
Ø Inaccurate estimates
Release 2 of the GANA System-Requirement Gathering
Planning and development of an advanced navigation system using PERT.
- Project manager
- Users own smartphones
- People use navigation systems
Ø Set up meetings with relevant stakeholders
Ø Start discussions on the basic requirements
Ø Elaborate and improve understanding of the requirements
Ø Finalize requirements
Ø Document requirements
Ø Send for final approval
Ø Get approval
Ø Disagreements resulting in a delay in gathering requirements
Industry Application: Case Study
Subproject: Extension of the Storage Capacity of Treated Water
Vlaamse Maatschappij Voor Watervoorziening (VMW), a Flemish water distribution company, used PERT on a project at the water production center (WPC) of Kluizen, Belgium. This center produces and delivers water by transforming surface water into drinkable water. It then distributes it to the customers by taking several different steps.
The VMW project was aimed at expanding the production capacity of water in East Flanders to address scheduling problems. It was a very capital-intensive project with a duration of more than six years.
The subproject extension of the storage capacity of treated water requires building two extra reservoirs for treated water (RWK). This will allow WPC to meet the daily demand of the customer.
To increase the storage capacity of pure water, VMW built two new reservoirs, each with a capacity of 15,000, installed pumps in a new high-pressure room to assure the circulation of the pure water, installed new high voltage cabinet for the increased energy requirement and built pipes between these new installations. With the help of these new reservoirs, they were able to satisfy demand during peak hours.
Using PERT, VMW was able to calculate the duration of all 26 individual tasks required for the completion of the subproject. PERT helped them in better scheduling of tasks and managing project deadlines by giving special attention to tasks on the critical path.
Geo-scientific Software Development Projects- Dishansh 2005
Dishansh 2005 is a software that calculates spatial relations by plotting planer and linear structural features, for seismological and geotechnical interpretations. Dishansh 2005 development team used PERT for planning, scheduling, and control of activities during the software development process. PERT was used as it allowed analysis and visualization of structural data following the same technique used in manual stereo nets.
PERT allowed the project managers to calculate the time required for the development of the software with some certainty. It also presented all the tasks in a logical manner and the duration required for the completion of each activity. Network diagram was constructed and the critical path identified. With the help of PERT methodology, Dishansh 2005 was able to predict that the probability of project completion within 60 days was 99.77%.
Is PERT Methodology Suitable for You?
As business varies according to type, size, industry, and many other factors, so do projects. Rather than looking for the best methodology, businesses should learn these methodologies, their uses, and applications and decide upon the best methodology for them according to the following variables:
- Organizational goals
- Core values
- Project constraints
- Project stakeholders
- Project size
- Cost of the project
- Ability to take risks
- Need for flexibility
PERT Methodology was designed for large, and complex projects. It is the preferred method for projects when time is of the essence but calculating it involves uncertainty. By its very nature, it is suitable for projects that are perhaps not very common or consists of large complex activities.
The PERT Methodology helps project managers make sense of complex procedures, that might involve activities that they are unfamiliar with. Alternatively, it can help to graphically organize tasks and activities.
If your entire team is working on a large multi-faceted project, PERT will help in the visualization of the order of tasks, milestones, and phases within a project. This will help you coordinate work across teams and departments more effectively by identifying the nature of the tasks: dependent, or sequential tasks or non-dependent, or concurrent tasks.
Table 1: PERT Checklist
|Visual Representation of the whole project life||Yes|
|Determines Activities Sequence||Yes|
|Long term Projects||Appropriate|
|Cost estimation||Not Covered|
|Guarantee of success||Hight|
Project management methodology is vital for today’s businesses. By using an appropriate style for your business, you can transform the way your team collaborates, works on tasks, and accomplishes project milestones.
nTask and PERT
Even with the help of PERT, project management can be overwhelming. For large and complex projects any miscalculation or accidental omission will leave you bewildered. Using project management software like nTask will ensure that you will not get overwhelmed by the size or duration of the project.
nTask allows you to easily manage your complex project by breaking down events into tasks and subtasks. It allows for better collaboration by making it easier to delegate tasks. nTask also helps in providing greater visibility and understanding of project variables such as timeline constraints, resource availability/utility and potential risk areas as identified by PERT. Furthermore, any changes in any task are shared in real-time with the whole team. The automated process reduces the chances of errors and mismanagement.
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