Critical Path Method (CPM) and Program Evaluation and Review Technique (PERT) are both project management techniques used to plan, schedule, and control projects. While they share similarities, they also have key differences. Here’s an overview of the distinctions between CPM and PERT:
- Focus on Time:
- CPM (Critical Path Method): CPM is primarily focused on the time required to complete each activity in a project. It identifies the critical path, which is the sequence of activities that determines the total project duration.
- PERT (Program Evaluation and Review Technique): PERT places more emphasis on the relationship between time and uncertainty. It uses a probabilistic approach to estimate the duration of activities, considering optimistic, pessimistic, and most likely time estimates.
- Estimation of Activity Duration:
- CPM: CPM typically uses a single, deterministic estimate for each activity’s duration. This estimate is based on historical data or expert judgment.
- PERT: PERT incorporates a range of time estimates for each activity—optimistic, pessimistic, and most likely. These estimates are then used to calculate an expected (mean) duration and standard deviation.
- Calculation of Project Duration:
- CPM: In CPM, the project duration is determined by the critical path—the longest path through the network of activities. The critical path represents the minimum time needed to complete the project.
- PERT: PERT calculates the expected duration for each path and considers the variability in activity durations. The project duration is often expressed as a probability distribution.
- Activity Dependency:
- CPM: CPM assumes that activity durations are known with certainty, and it uses a deterministic approach to project scheduling. Dependencies between activities are based on logical relationships.
- PERT: PERT allows for uncertainty in activity durations and considers probabilistic dependencies. It takes into account that some activities may be more uncertain than others.
- Use Cases:
- CPM: CPM is often used in projects where the time estimates are relatively certain, and there is less uncertainty in the project schedule. It is well-suited for projects with a focus on time efficiency.
- PERT: PERT is particularly useful in projects where there is a high degree of uncertainty in activity durations. It is commonly applied in research and development projects or projects with a high level of innovation.
- Deterministic vs. Probabilistic Approach:
- CPM: CPM is a deterministic model, meaning it assumes that activity durations are fixed and known with certainty.
- PERT: PERT is a probabilistic model, considering the variability in activity durations and providing a range of possible project durations.
In practice, a project manager may choose to use CPM, PERT, or a combination of both methods based on the specific characteristics and uncertainties associated with the project at hand.