Network Charts: What's the Difference between PERT and CPM?

Summary

This video explains the key differences between the Program Evaluation and Review Technique (PERT) and the Critical Path Method (CPM), two project management tools that emerged in the 1950s. PERT, developed by the US Navy, is ideal for uncertain, high-risk projects, using probabilistic time estimates. CPM, developed by Dupont, is more suited for familiar, repetitive tasks and uses deterministic estimates. The video also highlights how advancements in software and AI have blended both methods, making them more adaptable for large-scale projects while reducing the need for detailed estimates in smaller or agile projects.

Takeaways

• 😀 Per and CPM are two project management tools that emerged in the 1940s, originating from the Manhattan Project, but they calculate schedules differently.
• 😀 The main difference between the Program Evaluation and Review Technique (PERT) and Critical Path Method (CPM) is in the way they represent activities and estimate durations.
• 😀 PERT represents activities as lines with nodes showing dependencies, while CPM uses nodes in boxes connected by arrows to depict the sequence of activities.
• 😀 PERT uses three-point estimates for activity durations: optimistic, most likely, and pessimistic, providing a probabilistic approach, while CPM uses single-point estimates for more predictable durations.
• 😀 PERT is more suitable for projects with high uncertainty, like R&D or novel tasks, whereas CPM is used in more predictable environments like construction projects.
• 😀 The PERT method helps optimize and control schedules by analyzing possible outcomes, while CPM also factors in the budget and trade-offs between schedule and cost.
• 😀 CPM was designed to manage both schedule and budget, with concepts like critical/non-critical activities and float, while PERT focuses purely on schedule management.
• 😀 PERT is commonly used in research and development sectors where innovative projects are happening, while CPM is predominantly used in construction sectors.
• 😀 The differences between PERT and CPM are becoming less relevant due to modern project management tools, which can handle these calculations automatically.
• 😀 With increasing use of AI and software tools, project managers now rely on automated systems to make estimates and perform calculations, reducing the need for detailed understanding of these methods.

Q & A

What is the difference between PERT and CPM?

Both PERT (Program Evaluation and Review Technique) and CPM (Critical Path Method) are used for project scheduling, but PERT is a probabilistic method while CPM is deterministic. PERT is suitable for uncertain, novel, or high-risk projects, whereas CPM is used for more familiar and repetitive projects.

When were PERT and CPM developed?

Both PERT and CPM were developed in the 1950s. PERT was created by the US Navy with consultants from Booze Allen Hamilton, while CPM was developed by Dupont and Remington Rand in the commercial sector.

How do PERT and CPM represent activities in a project?

In PERT, activities are represented as lines, with nodes showing the relationship between activities. In CPM, activities are represented by nodes written into boxes, with arrows or lines indicating the sequence of dependencies between activities.

How do PERT and CPM estimate the duration of activities?

PERT uses three-point estimates for the duration of activities: optimistic, most likely, and pessimistic. These estimates are then averaged to determine a more balanced expected duration. CPM, on the other hand, uses a single-point estimate for the duration of each activity.

What is the typical formula used to calculate the expected duration in PERT?

The common formula used in PERT to calculate the expected duration is: (Optimistic estimate + 4 * Most likely estimate + Pessimistic estimate) / 6.

Why is PERT considered more appropriate for high-uncertainty projects?

PERT is considered more appropriate for high-uncertainty projects because it takes into account the variability in activity durations using three-point estimates, making it a probabilistic approach suitable for projects with unknown or unusual factors.

How is CPM different from PERT in terms of project predictability?

CPM is deterministic, meaning it assumes more predictability and certainty in project activities. It works well for projects with well-defined activities where the duration is easier to estimate with confidence, making it more suitable for familiar and repetitive projects.

What sector typically uses PERT, and why?

PERT is commonly used in the research and development (R&D) sector because it is designed to handle novel, high-risk, and uncertain projects that may involve new or untested activities.

What was the original purpose of CPM?

CPM was originally developed to control both schedule and budget by analyzing trade-offs between the two. It includes concepts like critical and non-critical activities, float, and dependencies to help manage project timelines and resources effectively.

How has the use of PERT and CPM evolved in modern project management?

With the advancement of software tools and AI, the differences between PERT and CPM have become less pronounced. Software now automates much of the scheduling and estimation work, and tools often integrate both methods, making the traditional distinctions less relevant.