In the 1950s, the U.S. Navy created a statistical project management tool, the "Program Evaluation and Review Technique," to help manage large and complex projects. The PERT system uses charts to scope out the individual components of a project in a logical order, showing relationships between activities. These charts also use critical path analysis that helps you create schedules that will make your project go more smoothly. While PERT makes it easy to visualize your project's activities and timelines, there are some disadvantages with data quality and the lack of emphasis on non-critical tasks.
Advantage: Project Visualization
If you were building a computer, a PERT chart would show how your project is broken down into activities, such as installing the motherboard and adding hard drives. Your project team sees all the steps needed to make the computer. Each team member also clearly sees his or her own activities and responsibilities, whether it's installing a part, connecting wires or adding software. It's this transparency that makes sure nothing slips through the cracks. PERT charts also outline the relationships and dependencies between individual project activities, helping you understand the order of work. For example, the chart would show that you need to have the computer's motherboard installed before you could start connecting other hardware to it.
Advantage: Critical Paths
PERT creates timelines, or paths, showing the steps needed to reach your project goal and how long it will likely take to finish. This allows for the fact that projects do not always go as planned by setting weighted timelines based on optimistic, probable and pessimistic estimates. The critical path is the longest timeline. With the computer example, the critical path shows the shortest time the building process can take and keeps you focused on the most important activities. You can identify delays or issues quickly and may be able to divert resources from less important paths, such as installing accessories, to bring your critical path back up to speed.
Disadvantage: Data Quality
Your PERT chart breaks your project into independent activities. It requires accurate and consistent data to establish resources, relationships and deadlines. If you hadn't built a computer before, you might not be able to break down the activities cleanly, and you may have problems getting precise data for complex projects as well. For example, it is hard for project teams to give accurate time estimates for activities that are new to them. If some of your team members aren't familiar with installing certain hardware in a computer, then the timeline may end up based on opinions rather than accurate estimates. Even if you're confident that you control internal data, external factors may cause problems. If a supplier does not deliver a key computer part on time, you may need to modify your chart.
Disadvantage: Critical Path Emphasis
While PERT encourages you to focus on the critical path, you may run into problems if you ignore activities on other paths. These might grow in importance over time, especially if there are delays or problems that then affect the critical path. For example, if an activity to install a piece of computer hardware on a shorter path overruns, you may have to put your critical path on hold until you get back on track, which extends your timeline. If that part doesn't get installed quickly and causes the deadline to extend a lot, it may become your new critical path, and you may need to modify your project analysis.