I continue to understand project management techniques. Next in line is the critical path method (CPM or Critical Path Method), a project planning method that helps to meet deadlines and meet budgets even on complex projects.
What is the essence of the critical path method
The method is based on the search for a "critical path" - the longest sequence of interrelated tasks. These tasks are called critical because any delay in them will result in delays in project completion. Therefore, special attention should be paid to these tasks.
By identifying critical tasks, you will also figure out tasks that can be moved without affecting the project timeline in any way. The time of these tasks is added to the so-called total time reserve..
When and how did CPM appear?
The history of the critical path method goes back to the 40s of the XX century, to the Manhattan project. It was then that the chemical company DuPont, which took part in the project, developed the first methods that formed the basis of CPM.
Later, in the 1950s, Morgan R. Walker of DuPont proper and James Kelly of Remington Rand, in an attempt to figure out how to reduce the costs of poor planning, came up with the critical path method. Around the same time, the US Navy and Booz Allen Hamilton developed the PERT method (I'll talk about it sometime), which also includes the concept of a "critical path". That is why these two methods are often used together.
By the way, for the first time the critical path method was used in the construction of the World Trade Center in New York (those very “twin towers”).
How to determine the critical path
The main task is to create a visual model of work on the project for further analysis. For this, you can use, in principle, anything - even simple graphs, even Gantt charts, even flowcharts.
But the visual model needs data, so the first step is to collect it.
- Write down all tasks. You can use decomposition for this, but don't overdo it - the final list should include important tasks needed to complete the project, without strong details, otherwise there will be too many tasks, and the analysis of the critical path will take a very long time.
- Figure out how much time each task will take. This is almost a key point - without it, you will not be able to find out the maximum time that it will take to work on a project along the critical path. It will be possible to estimate the time only approximately, based on your experience and the experience of colleagues. It will also be helpful to write down approximate dates when each task should start and end.
Determine how the tasks are related to each other, when one task affects the start date of the next, etc. To do this, for each task, answer yourself the following questions:
- What should be done before moving on to this one?
- What will need to be done immediately after it?
- What needs to be done along with it?
When you have all this data in hand, you can already create a visual model and use it to determine the critical path of the project - the longest path leading to the completion of the project, and the earliest and latest deadlines when tasks will not delay the project. As I said, a project may have more than one critical path, because different chains of actions can run in parallel.
And although it seems that among all tasks, only those on the critical path are important, this is not so. Tasks on the critical path are not always important, and tasks outside it can be very important.
About resource restrictions
Usually, these graphs are built on the basis of logical connections to determine the critical path. But logic is not always the only limitation. There may be others related to project resources: time, people, etc.
Let's say if you work in a team, you can divide the tasks between the participants, thus paralleling them. But if you work alone, a resource constraint arises - you cannot break apart and do two things at the same time, so the critical path will be different.
Advantages of the critical path method
There are significant benefits to using CPM in project management. The method helps the project manager:
- Identify the most important tasks in order to understand what needs to be paid more attention. If the deadlines for at least one important task are screwed up, the entire project will suffer from this.
- Reduce project time. By identifying the tasks that together add up to a common time reserve, you will clearly understand where you can find “extra time”. Well, just in case.
- Assess the risks. If you know how tasks are related to each other, it is easier to predict the impact of a missed deadline on one task on the result of the next.
- Compare plan with reality. Having defined the critical path, you get a detailed plan that you need to follow. This makes it very easy to keep track of how the actual work on the project deviates from the planned one. You can identify problem areas and get rid of them.
Disadvantages of the critical path method
The disadvantages of the method follow from its advantages.
- Tasks in the project take all the time allotted for them.
- If you finish one task ahead of schedule, it will not always be possible to finish the entire project ahead of schedule. Time and other resources are too rigidly distributed.
- The general reserve of time will definitely take place, it is impossible to get rid of it and reduce the project time.
- It is not applicable everywhere.
- The complexity of applying the methodology in solving creative problems - how to predict the timing of the project due to the huge number of unstable variables?
- Difficulty in using CPM in projects with high execution risks.
Who is the method for?
By the way, about applicability. In general, the search and analysis of the critical path can be used in any project: from software development to construction. But in creative projects or startups, where there are a lot of uncertainties, it will not work to use the critical path method - the timing simply cannot be predicted.
CPM will suit you if the actions that need to be completed within the project:
- ordered and executed sequentially,
- can be stopped and started independently of each other, within a chain of tasks.
In short, the critical path method is a way to determine the maximum amount of time it will take to complete a project. Knowing it, you will be able to build an optimal project schedule (not necessarily complex - this is some kind of far-fetched limitation) in order to do everything on time and at minimal cost.
However, it is not necessary to implement the method completely. If you see a benefit for the project in some individual elements of the critical path method, you can easily integrate them into your project management process. Flexibility and adaptability are extremely important for any modern specialist who wants to be in demand. For a project manager, no less.