Project management is a complex domain that requires various specific skill sets and competence. You can see it clearly in the way the Project Management Institute has organised the Project Management Body of Knowledge (PMBOK).
Project time management is an essential project management area of knowledge. It encompasses all the processes a project manager must accomplish to ensure timely project completion, which is, in turn, crucial because it is a hallmark of project success.
One of these processes is schedule development. It determines the start and end dates of the project and its activities or tasks. In other words, schedule development leads to the creation of the project schedule.
Schedule network analysis is a technique you can use to generate the project schedule. It allows you to identify the tasks that must be accomplished to complete the project, how they are interconnected, and how they must be sequenced and scheduled.
This is where critical path analysis comes in. The critical path method (CPM) is a specific schedule network analysis technique.
What Is the Critical Path Method?
The critical path method involves breaking down a project into individual tasks, identifying their dependencies, and mapping out the sequence of these tasks to determine the project timeline and how the project components must proceed against this timeline.
Ultimately, the goal is to generate a ‘critical path diagram’. This is a visualisation of a project’s ‘critical path’ – i.e., the shortest amount of time from project start to completion (the minimum project duration) – and, thus, the expected project end date.
Critical Path Analysis Steps
How do you perform critical path analysis? Here’s how:
1. Identify Individual Activities Through a Work Breakdown Document
Begin by listing all the specific tasks required to complete the project. Organise them into a work breakdown structure (WBS) based on deliverables or project phases for easy visualisation.
A WBS drills down to individual tasks. For instance, if you’re building a house, you can break down the work into the following phases:
- Design
- Procurement
- Construction
- Inspection
- Turnover
Every phase will have individual subcategories. For instance, under design, you’ll need permits and drawings. Drawings can be broken down into:
- Architectural drawings
- Engineering drawings
- Structural drawings
- Technical drawings
- Mechanical, electrical and plumbing (MEP) plans
There are various types of architectural drawings, so relevant individual tasks can include:
- Concept drawings: These are the initial sketches.
- Site plans: They situate the building in their environment and provide a bird’s eye view of the construction
- Floor plans: They provide the layout of the interior and show how the space will be utilised
- Finishing drawings: They indicate the finishing elements that will be used, including the paint colour scheme, the paints and coatings to be used, the flooring and wall materials, the ceiling type and design, etc.
2. Establish Dependencies
Next, determine the dependencies between tasks. Dependencies define the relationships among activities. If activity N requires the output from activity F, activity N cannot proceed unless activity F has been completed.
Suppose you’re developing a mobile application and have identified the following tasks:
- Requirement analysis
- UI and UX design
- Backend development
- Integration testing
- Deployment
In this case, backend development depends on requirement analysis and UI/UX design. It cannot start before these two predecessor tasks have been completed.
Dependencies can be classified into four types:
- Finish-to-Start (FS): Task B cannot start until Task A finishes.
- Start-to-Start (SS): Task B cannot start until Task A starts.
- Finish-to-Finish (FF): Task B cannot finish until Task A finishes.
- Start-to-Finish (SF): Task B cannot finish until Task A starts.
3. Estimate Task Durations
Once the dependencies have been identified and defined, estimate the duration of each task. Accurate task duration estimates are critical because they directly impact the project and critical path duration.
In the example mobile app development project used above, the task duration estimates can be:
- Requirement analysis: 5 days
- UI/UX design: 10 days
- Backend development: 15 days
- Integration testing: 7 days
- Deployment: 3 days
The individual duration estimates are the foundation of your project schedule, so be systematic when calculating duration estimates. You can use your expert judgement to assign the number of hours or days to individual tasks or use other approaches, including analogous, parametric, three-point, and bottom-up estimation.
4. Visualise the Sequence and Dependencies of Activities
Once you have a list of tasks, task dependencies and task duration estimates, plot them all in a network diagram. This will help you visualise the sequence of activities, which will then help you accomplish the next step.
5. Identify the Critical Path
Calculate the earliest start (ES) and earliest finish (EF) dates for every task, as well as its latest (LS) start and latest finish (LF) dates.
- ES: What’s the earliest date the task can start?
- EF: What’s the earliest date the task can finish?
- LS: What’s the latest date the task can start?
- LF: What’s the latest date the task can finish?
The difference between the earliest and latest values (e.g., LS-ES) is the float for that activity. The float is the number of days an activity can be delayed without pushing back the earliest start date of a dependent or succeeding activity. If an activity has zero float or zero flexibility in its start date, it is on the critical path or is a critical task.
The critical path duration is the sum of the individual durations of all critical tasks. Therefore, if the key activities identified in the app development example above are all critical tasks – assuming there are no other critical tasks apart from these – the critical path duration is 40 days. It’s computed as:
- Requirement analysis: 5 days (Critical)
- UI/UX design: 10 days (Critical)
- Backend development: 15 days (Critical)
- Integration testing: 7 days (Critical)
- Deployment: 3 days (Critical)
That’s 5 + 10 + 15 + 7 + 3 or 40 days. Therefore, the hypothetical app development project requires at least 40 days to complete or has a minimum project duration of 40 days.
6. Iterate and Adjust
Critical path analysis leads to a project schedule. However, a project schedule is not set in stone. Throughout the project life cycle, you’ll find yourself iterating the critical path analysis and adjusting your critical path as unavoidable and unexpected incidents happen.
Learn Critical Path Analysis
The critical path method is an essential schedule management tool. It identifies and focuses your attention on the critical tasks or those that can delay your project.
Applying CPM allows you to identify and respond to potential delays, optimise your resources and, ultimately, deliver the project on time.