Situation: You need a quick description of how you can leverage CPA on your project.
Our Techniques Wiki offers a library of commonly used approaches to tactical challenges on your project. Critical Path Analysis is a pretty well used technique, so I thought it would be useful to highlight it here and get your take on our "official version". The beauty of posting it as a wiki is that it's community driven and refined. If you think it should change - you can change it.
'An analysis technique used to identify the critical (essential) and non-critical (non-essential) activities associated with a business process or work plan and the amount of float (slack) associated with each noncritical activity'. The result of the analysis defines the critical path, a sequential set of related and essential steps that comprise a value stream or work plan. It is the longest path, in terms of duration, that passes through all the critical steps of a value stream or work plan, and determines the fastest time to completion. The results of critical path analysis are depicted graphically in a Critical Path Diagram.
- To identify the critical and non-critical activities associated with a business process or work plan.
- To identify non-critical steps which can be eliminated, at minimum cost, to improve the value stream or work plan.
- To identify the amount of time an activity may be delayed without affecting subsequent, dependent activities or the ending time or date.
- Identify all steps in the business process or work plan.
- Document the steps in the sequence in which they occur.
- Identify the relationships between steps, and document the dependencies between them.
- Determine the latest allowable start and end time or date at which each step can occur without delaying the next step and, subsequently, the whole value stream or work plan.
- Assign a float value to each task. Critical tasks should have zero float. Non-critical tasks will have a numeric value associated with them, representing slack time.
- Calculate the float for each step by subtracting the Early Start time or date from the Late Start time or date and assign a float value to each task and sub-task.
- Using the information collected above, identify the critical and non-critical tasks and sub-tasks by determining the duration of the value stream or work plan.
- Chart/document the critical path.
The essence of critical path analysis is to examine all options for reducing the duration of time required to complete the critical steps in a business process or work plan. Tasks, their duration, and their dependency relationships determine the critical path. When applied in business reengineering, critical path analysis addresses issues of quality, efficiency, and cost reduction by standardizing work efforts and eliminating unnecessary steps to reduce the time required to satisfy the customer of the value stream. In project planning, it is applied to determine all options (duration, cost, resource requirements) for reducing the work plan or project duration and for determining the amount of time an activity may be delayed without affecting subsequent, dependent activities or the project end date. When used in conjunction with Cycle Time Analysis andDependency Analysis, Critical Path Analysis is an effective tool to measure the quality of the business process or work plan by analyzing the steps in the path, measuring inefficiencies, and determining what steps can be eliminated to improve a business process redesign or reduce the amount of time required in the work plan.
Critical path analysis begins with the identification of all activities (tasks and sub-tasks) which are part of the business process or work plan. Document the tasks and sub-tasks in sequential order; documentation can be prepared using various diagramming techniques such as block diagrams, work flow diagrams, etc. (see Work Flow Diagramming), in a simple list, or using a automated project management tool for creating work plans.
Once all tasks and sub-tasks have been identified, identify the relationships between the tasks and sub-tasks, usingDependency Analysis. Determine which tasks and sub-tasks are dependent upon one another and establish a predecessor or successor relationship. Document these relationships on the diagram, list or work plan.
Determine the critical and non-critical activities by assigning a float value to each task and determining the float associated with each task and sub-task. Float represents slack time, the amount of time an activity may be delayed without affecting succeeding activities (free float) or the ending duration or date (total float). Critical tasks should have zero float as there should be no slack time associated with them. Critical tasks must be accomplished sequentially and promptly; thus, when a critical task is delayed, the completion and duration of the business process or the end date of the project is affected. Non-critical tasks and sub-tasks have a numeric float value associated with them, as there can be slack time without affecting the end result. This value (e.g., float value of 1=slack time of 1 unit of time that is being measured) represents the amount of delay that can occur without affecting the duration of the business process or the work plan. To determine the float associated with each task or sub-task, define the early start and early end duration or date for each task or sub-task (e.g., the earliest possible time each task and/or sub-task can begin and end). (See also Cycle Time Analysis.) Calculate the float for each step by subtracting the early start time or date from the late start time or date.
Chart the critical path by identifying all critical steps (those with zero float). The path through all steps or events that have zero float represents the critical path. The non-critical steps (those with associated float) are candidates for elimination from the value stream or work plan.
Although resource constraints do not affect true critical path calculation, critical path analysis may be followed by resource planning, using resource manipulation techniques such as Resource Allocation, Loading and Leveling to improve project schedules and end dates.