Performing critical path analysis
Critical Path Analysis is a technique for analyzing, planning, and understanding the schedule for large, complex projects with multiple constituent parts.
Early iterations of Critical Path Analysis can be traced back to the Manhattan Project in the 1940s, the project that gave the world the atomic bomb. Given the ambition, scale, and importance of this world-altering project, its leaders and participants developed several techniques to ensure that all the tasks involved in such a feat, were understood and sequenced properly. Getting it wrong meant potentially going too early and letting slip to the enemy before they were ready; allowing time to run its course without influencing progress on the project could have meant devastating consequences. Time was of the essence but so was quality.
Most of us aren’t attempting near so dangerous and vital, but still, anything larger than a few simple tasks, quickly becomes a nebulous series of activities and it can be very hard to spot which tasks must be done sequentially, which can be run alongside other tasks, and which sequence effectively determines the overall timeline and finish. There are hints of knowing what your MVP is in here too. It’s tempting to call everything critical, but it never is.
There will be parts of a project which you can allow to shift about in the timeline and not worry about – they won’t affect the finish line. Others need close attention. There will be parts of your project which you can forego if you find they are adversely affecting your timeline.
How long a project takes depends therefore on the longest sequence in the project plan. Mapping out tasks, their duration and their dependencies allows you to obtain a reasonably confident estimate of the project’s overall timeline and highlights which sequence must be monitored most closely to maintain the shortest timeline.
What is critical?
To spot my critical path, I like to think of ‘critical’ in four ways:
A task is critical if it must be performed for the project to be considered complete or a success.
Example: If you’re a chef in a restaurant, and the customer ordered a meal comprised of roast chicken with roast potatoes, green beans, steamed baby carrots and gravy, all the elements of the customer’s dish must be provided; you cannot deliver a meal without any of these components.
A task is critical if it forms part of a specific order (i.e. something else depends upon it)
Example: If you’re building a house, you can’t construct the walls and then dig the foundation; you must do it sequentially.
A task is critical if it is a cornerstone for multiple other tasks, and any delay will cascade down the completion of the entire project.
Example: If you’re organising a conference, securing the venue is a fundamental aspect of the conference. Without a confirmed venue, other key tasks such as sending invitations, planning the layout, and arranging catering and technical equipment cannot proceed. Any delay in securing the venue will directly delay multiple subsequent tasks, such as marketing the event, finalizing the agenda, and coordinating with speakers and vendors.
A task is (often, not always) critical if it has a fixed elapsed time or duration
Example: If you’re an extreme deep sea diver, returning to the surface requires a slow and controlled decompression process to avoid decompression sickness (the bends). The decompression time is typically one day per 100 feet of seawater, plus an additional day. For example, a dive to 650 feet would require approximately eight days of decompression. This careful and prolonged process ensures the safety and health of the divers as they adapt to and return from extreme underwater pressures and cannot be expedited.
Critical Path Network Diagram
One of the easiest methods I find for critical path analysis, is to transpose your project plan into a network diagram, adding time estimates for each task, indications of fixed duration, arrows indicating hard dependencies, and milestones.
Follow the lines, adding as you go, and identify the longest sequence in your network – this is your critical path. By the end, you should have something that may look like this:
To help with this, I have a slide on a plain slide deck that you can use to get you going - download using the button below.