At this point, you now know the basics of project management and how it works. Now you are ready to take things to the next level with critical path analysis diagrams. This blogpost will teach you what critical path analysis is, what purpose it serves, and how to create the diagrams.
What is Critical Path Analysis?
First things first, we have to define what critical path analysis is. According to the book, Information Technology Project Management by K. Schwalbe, critical path analysis (can also be called the critical path method, or CPM) is “a network programming technique used to predict total project duration” (Schwalbe, 2018). In other works, it is used to manage project schedules, and to make sure schedules don’t become overrun.
The CPM consists of the critical path itself, as well as stacks (also known as floats). The critical path is defined as “the series of activities that determines the earliest time by which the project can be completed” (Schwalbe, 2018). A stack/float is how long an activity can be delayed without delaying the activity that follows or the project finish date. All that being said, critical paths are the longest paths through the network diagram and they have the least amount of slack.
How do I Calculate the Critical Path?
Before going over how to calculate the critical path, it is important to understand what is included in the critical path method. According to ProjectManager.com, the CPM includes:
Identifying all tasks necessary to complete the project and all dependencies between each task
Estimating how long each task will take to complete
Calculating the critical path based on the duration of each of the tasks and dependencies and identifying which activities are the most critical
Focusing on scheduling and controlling the most critical activities
Creating project milestones and setting deliverables
Setting the stakeholder’s expectations in regards to deadlines
ProjectManager.com lists eight important steps when calculating the critical path. They are:
Collect the Activities. Use a work breakdown structure (also known as WBS) to collect the project activities and tasks that lead to the final deliverable.
Identify the Dependencies. Make sure you figure out which tasks cannot be started until other tasks are completed.
Create a Network Diagram. Use a network diagram to show the order of activities.
Estimate Timeline. Estimate how long each activity will take.
Use the Critical Path Algorithm. The critical path algorithm has a forward pass and a backwards pass.
The Forward Pass: Determine the earliest start time and the earliest finish time by using the network diagram and the duration of each activity. The earliest start time is equal to the earliest finish time of the previous activity. The earliest finish time is calculated using the following formula: Earliest finish time = earliest start time + activity duration. The earliest finish time of the last activity is equal to the estimated time it would take to complete the whole project.
The Backward Pass: Assign the last activity’s earliest finish time as its latest finish time. Then use the following formula to calculate the latest start time: Latest start time = latest finish time - activity duration. For the previous activities, the latest finish time is the smallest of the start times for the following activity.
Identify the Float of Each Activity. The formula for calculating the float is: Float = latest start time - earliest start time.
Identify the Critical Path. The activities where the float is equal to 0 are part of the critical path.
Update During the Execution. Make sure you update the critical path network diagram as needed as you work on the project. More on why this is important later.
Shortening Project Schedules
Sometimes a project schedule estimate can be longer than what the stakeholders want. It is not uncommon for stakeholders to want to reduce the estimated time the project will take. One technique that is used to do this is called crashing. According to K. Schwalbe, “crashing is a technique for making cost and schedule trade-offs to obtain the greatest amount of schedule compression for the least incremental cost” (Schwalbe, 2018). This technique comes with pros and cons. The pros of crashing are that it reduces the time it takes to finish a project. The cons are that it can, and often does, increase the total costs of a project.
Another technique that is used to shorten a project schedule is called fast tracking. Fast tracking “involves doing activities in parallel that you would normally do in sequence” (Schwalbe, 2018). So, instead of waiting for one task, or tasks, to be completed before starting the next one, you would go ahead and start the next activity even though the previous tasks are not quite finished yet. Just like the crashing technique, this method has its own pros and cons. The pros are that it can reduce the amount of time needed to complete the project. The cons are that it can increase the cost of the project. It can sometimes even lengthen the project schedule because starting tasks too early increases the project risk and can often result in reworking tasks.
Why is it Important to Update Critical Path Data?
As stated before in step 8 on how to calculate the critical path, it is important to update the project schedule with actual data. When updating the project schedule, when activities are completed, make sure you document the actual duration of each activity. Also list any document any new duration estimates for activities in progress or ones that haven’t been started yet. The reason this is important is because the critical path can change based on the actual data and the new estimates, which can change the new estimated timeframe the project will be completed by. Make sure stakeholders are kept informed of any changes made to the estimated duration times.
Why is the Critical Path Important in Agile?
The critical path is essential in the agile method. Why? Because the critical path is the path that takes the longest to complete. When working with agile, it is a good idea to try to keep the critical path the as close to original as possible. The reason is because any unexpected changes that impact the critical path will change the entire timeline of the project.
Example
The chart below shows an example of what a critical path analysis diagram looks like. Notice the critical path outlined in orange.
References
Schwalbe, K. (2018). Information Technology Project Management (9th ed.). Boston, Massachusetts: Cengage Learning.
Westland, J. (2021, January 25). Critical Path Method: The Ultimate Guide to Critical Path. Retrieved October 2, 2021, from https://www.projectmanager.com/critical-path-method
Comments