The critical path method (CPM) is a project management tool developed in the U.S. in 1957. CPM may not be appropriate for all projects. Users should be aware of its capabilities and limitations, and implement it correctly.
In the critical path method, a project is broken down into sequential, interconnected activities. Each activity is assigned a completion time. The activities are linked, in graphical view, to show all possible paths to completing the project, and the shortest duration “critical path.”
CPM is not suitable if projects cannot be broken down into discrete activities with known completion times. For example, on a new project, activity durations may be hard to estimate.
Critics note that it takes too much time to identify all activities and inter-relate them to get multiple project paths. This causes user frustration ahead of the project.
CPM stops working in practical situations in which employees are often re-allocated across projects and activities. This reallocation changes activity completion time and disrupts the CPM plan.
Identifying a single critical path is difficult when there are parallel paths with similar durations. Project teams may disagree on which path to choose or which activities are more critical than others.