When working on complex multi-phase projects with multiple stakeholders, many organizations use established project management methods to ensure they are meeting their goals on time and on budget. The Program Evaluation and Review Technique (PERT) or Critical Path Method (CPM) are two techniques organizations can leverage to manage their projects. Both have their strengths and weaknesses based on what kind of project they are being used to manage.
Sometimes, PERT and CPM are used in tandem to manage projects which have several relationships and dependencies between activities. PERT is typically used for research and development projects, whereas CPM is commonly used for construction-based projects.
Factoring in the Knowns and Unknowns
One of the key differences between PERT and CPM is how they treat the knowns and unknowns of a project. PERT is typically used to manage the uncertain activities within a project, which is why it often works well in research-based environments where the outcomes are uncertain. CPM, on the other hand, is used to oversee the well-defined activities of a project.
PERT works best for jobs or activities that are non-repetitive in nature, whereas CPM is the opposite. It is typically best for repetitive jobs where the outcome or result is predictable or known.
Taking into Account Time and Cost
Time and cost are two of the most important factors organizations consider when working on large-scale projects. CPM and PERT both treat time and cost differently. In PERT, time is the major factor that is controlled and monitored. Cost is not considered. Using PERT, organizations can pinpoint three precise time estimates for activities within the project. Those estimates take into account possible delays that can occur. Because PERT deals with unpredictable activities, it is imperative to have multiple time estimates for the project. To calculate the expected time to complete the project, the most likely scenario is multiplied by four, adding the most optimistic and pessimistic times and then dividing the result by six.
CPM is a method that controls both time and cost and evaluates the time-cost trade-off for activities within the project. Unlike PERT, CPM provides only a one-time estimate, which is possible because CPM deals with activities that are repetitive in nature and have known outcomes. Instead of a high-precision time estimate as in PERT, CPM time estimates are fairly reasonable. Critical and non-critical activities are differentiated in CPM, but not in PERT. To calculate the critical path using CPM, all of the required tasks are listed with a time assigned to each task and dependencies between the activities. The longest path from beginning to end is calculated with the earliest each activity can start and the latest it can finish without causing delay.
Deciding on the Best Method for Your Project Between PERT and CPM
Deciding which method to use for your project will depend on what kind of activities you will need to manage. PERT versus CPM is a hard decision to make, but it will come down to the important factors of whether your organization is dealing with knowns or unknowns, and considering both time and cost or just time.
Each technique helps organizations to manage risks, mitigate delays and ensure efficient completion of projects.