Project Management

Why critical path is critical to project management

If the PMBK definition of critical path has you puzzled, read Dr. Andrew Makar's explanation of this project methodology in real-world terms.

If the PMBK definition of critical path has you puzzled, read Dr. Andrew Makar's explanation of this project methodology in real-world terms.

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When I was a business analyst working on a human resource talent acquisition implementation, six weeks out from the launch date the project manager rushed us into a room and asked us to figure out the critical path. I had heard the term critical path before, but I didn't really understand what it meant. I knew the project was critical to the HR organization and thought everything on the project was on a critical path.

Project managers will be amused that we were trying to figure out the critical path with six weeks before launch rather than prior to project execution. In hindsight, the project manager should've known the critical path earlier and been monitoring the schedule's progress. I still find it puzzling that the project manager asked a bunch of business and system analysts to determine the project's critical path.

It wasn't until I shifted my career into project management that I gained a better understanding of the critical path and its impact to a project. The Project Management Body of Knowledge (PMBOK) defines the critical path as "the sequence of schedule activities that determines the duration of the project." Project managers can also apply the critical path methodology technique to "determine the amount of float on various logical network paths in the project schedule network to determine the minimum total project duration."

Critical path explained

If you're just as confused by the PMBOK speak as I was, let me restate it in a way that's easier to understand.

The critical path is simply all the tasks that determine the end date in your project schedule. If one of those tasks is late by one day, then your project end date will be extended by one day. Oftentimes, there will be tasks that are not on the critical path; this is due to the slack in the project schedule. If you refer to your current schedule, you can examine the Gantt chart and quickly identify the tasks that have some float compared to the tasks that have no slack.

Slack is the amount of time a task can be delayed without impacting the start date of a subsequent task. The critical path methodology is simply a technique to identify all the tasks that will directly impact the project end date. Figure A depicts a Gantt chart with a set of tasks on the critical path. Figure A

Critical path in Microsoft Project

In Figure A, there are five tasks in the project schedule and Task 4 is not on the project's critical path. If Task 1, 2, 3, or 5 is delayed, then the entire project will be delayed. If Task 4 is delayed, it has seven days of free slack before it will start having an impact on the schedule. Since Task 5 is three days in duration, Task 4 could have an actual duration of 10 days before it becomes part of the project's critical path. If it exceeds 11 days, Task 4 will create a new critical path.

I'll admit I'm reluctant to create a network diagram and start the forward and backward pass mechanics. Tools are invented for a reason and, fortunately, Microsoft Project can support forecasting, what-if analysis, and detailed scheduling metrics along the critical path. By switching to different views and formatting the Gantt charts, you can quickly identify and monitor the tasks on the project's critical path.

Figure B depicts the free slack in Microsoft Project. All the tasks on the critical path have zero slack in their schedule and that's why these tasks drive the end date. Task 5 has 7 days of slack and is not included on the critical path. By increasing or decreasing duration on specific tasks, you can see the adjustments in the critical path. Figure B 

Critical path free slack

In my next column, I'll show you how to identify the critical path in Microsoft Project and use the different views to monitor and track the critical path.

Critical path and network sensitivity

If you want to learn about the critical path and network sensitivity, read my article on Network Sensitivity and the Critical Path. The article features the sample Microsoft Project file if you want to experiment with adjusting the critical path.

Additional TechRepublic resources about critical path

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About

Dr. Andrew Makar is an IT program manager and is the author of How To Use Microsoft Project and Project Management Interview Questions Made Easy. For more project management advice visit http://www.tacticalprojectmanagement.com.

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