Implementing the Critical Path Analysis
The term Critical Path Analysis (CPA) is commonly used interchangeably with CPM, but actually describes the tasks involved in implementing the Critical Path Method. During the analysis, a list of activities is created, a timeline is allocated to each, and a flowchart is designed. A variety of project management diagrams are typically utilized for CPA, including PERT diagrams and Gantt charts.
Activities and Tasks
The analysis begins by listing all of the activities and tasks that must be carried out for completion of the project. Creating the list requires a detailed analysis of the activities involved in planning, initiating and implementing the project. Managers determine the comprehensiveness of the list depending on the importance of each task to the final result and deadlines. Activities may be critical, essential to the completion of the project, or sub-critical, important for the project yet independent of the other tasks. Experience and practice are useful in determining the level of necessary detail in the list.
Once the activities are listed, each task is placed in a sequence depending upon its reliance on the completion of previous tasks. Each activity is assigned a duration, then individual times for the events are added up to create the timeline for each sequence. The critical path is the sequence with the longest time interval. Activities that are not part of the longest chain are placed parallel to the critical path. Determining the timeline for each activity is not always simple, but the longest and shortest times for completion of each task must be estimated.
Float and Drag
Activities within the critical path are said to "drag" the timeline of the project because any interruption would delay the entire project. Drag is noted within the timeline as the maximum amount of time a task would take. Sub-critical tasks that are not part of the critical path are said to have "total float" because they are independent of the critical path timeline. The float time is the maximum length of time available for the completion of the sub-critical tasks. These float and drag times are usually noted on the CPA model next to the symbol for each task.
Originally CPA used Program Evaluation and Review Technique (PERT) charts to visually model timelines. These plans employ activity on arrow diagrams, with the events presented in a sequence and activities shown as arrows between events. However, now the most common visual representation for CPM is the "activity-on-node" diagram. This type of model shows each activity as a box or circle with arrows representing the relationships between them. Gantt charts are also widely used in Critical Path Analysis to display activities and timelines in bar graph format.
Interpretation and Use
CPA can help assure that a project is completed as quickly and efficiently as possible, however the effectiveness of the model depends on the inputs of the project manager. Care must be taken when creating the list of activities and also in predicting the timeline. Typically difficulties or delays will also be encountered, so managers must adapt the CPA to reflect the current developments. Building the model and timeline is not the end of the analysis. Managers should continually monitor the progress of the project and prioritize and alter planned activities to shorten the critical path when possible.
The CPA is used to create a usable visual representation of a project's activities and timeline before the project begins, but this is not the end of its use. As the project progresses, obstacles will arise and resources must be shifted to allow deadlines to be met. Wise project managers can reach their planned deadlines by use of extra resources and parallel completion of sub-critical activities.