Critical Chain Basics
Here's a "quick and dirty" high level view of some of the major concepts involved in Critical Chain approach to project management and why they do what they do....
It all really boils down to the fact that the way we manage for uncertainty in projects is at the core of improvement of project performance, defined as getting projects done both faster and with better reliability of the promised final project due date. TOC/CC suggests the shifting of focus from assuring the achievement of task estimates and intermediate milestones to assuring the only date that matters -- the final promised due date. As a matter of fact, the scheduling mechanisms provided by CC scheduling allow/require the elimination of task due dates from project plans. Its benefit is that it allows those who use it to partially avoid "Parkinson's Law;" i.e., work expanding to fill the time allowed. Take away the idea of time allowed, and you've got half the battle won. But how to do that is the question that requires us to look at some current common project practices.
Project tasks are subject to considerable uncertainty, from both the unknowns of the invention process (in development projects especially) and from the universal effects of "Murphy's Law." As a result, task estimates that make up project schedules can contain considerable "safety" in them to try to allow for these unknowns when planning the project. In addition, many project organizations are multi-project enterprises, with resources frequently working across projects on more than one significant task in any particular period of time. This practice of multi-tasking, unfortunately common in many project organizations in many industries, also leads to expanded project lead times because when a resource alternates between tasks/projects, the task times for an individual project are expanded by the time that is spent on the other projects' tasks. Project resources are aware that they're in this multitasking environment and so their task estimates are further expanded (even unconciously multiplied by factors of as much as two or three) to account for this practice in project task commitments. The combination of the effect of the multi-tasking environment and the need to cover uncertainty lead to "realistic" project task estimates that contain considerable "safety" above and beyond the actual work time required for a task, and subsequent project plans and commitments that include these expanded times.
The TOC approach addresses this expansion of project plans with two mechanisms. First, we remove the safety from the tasks, and aggregate it as "buffers" of time that are sized and placed in the schedule to protect the final due date of the project from variability in critical tasks and that protect critical tasks from variability in non-critical tasks that feed them. These buffers now allow us to shorten task time estimates to aggressive target durations, shortening the time within which resources strive to to achieve their tasks. These short target durations (approximately 50% confidence estimates, whose expected overruns are isolated from the actual project commitments by the buffers), also support the second mechanism. They are so short that the resources are uncomfortable succumbing to multi-tasking or other distractions. This behavior supports the additional requirement posed by the CC methodology for management to enable resources to focus on tasks and to eliminate the multiplying effect of multitasking on project lead times. This is intuitive to many of us -- we often isolate project teams from multitasking in special task forces or "skunk works" when projects are of special importance. What the TOC approach allows us to do is apply this common sense solution to the overall project environment.
OK, so we've reduced task estimates, but we still have these buffers that include the protection that was previously spread around and hidden in the tasks. Note that I mentioned using 50% confidence estimates for the task durations. That means that, if allowed to focus on the tasks, half of the time tasks will be done in less than the target plan and half the time they will take longer. Due to the statistical nature of this uncertainty of tasks, this leads those using the TOC approach to be able to use buffers that are significantly shorter than the sum of the safety that was spread around in the previous scheduling paradigm. After all, those that come in ahead of time will replenish the buffer that was consumed by those that took longer than expected, assuring the protection of the only date that counts -- the final project due date. So with the combination of reduced task estimates due to the aggregation of safety and the reduction of buffer size, overall project plans can be typically 20-30% shorter than traditional plans with similar initial risk.
There is also another benefit of the use of the buffers, beyond protection of due date performance. They aren't just passive chunks of time in the schedule, but arather also provide the project manager and/or team with a clear indication of the health of the project at any point in time. The tracking of the consumption of these buffers provides warnings and indications of potential problems far before the project promise is in real trouble, allowing development of recovery plans in an atmosphere other than one of crisis. Once a project plan is implemented and underway, TOC's "Buffer Management" provides built-in risk management and therefore enhanced reliability of meeting the project due date, even with the shortened overall project lead time.
As a summary for individual projects, the TOC approach, by viewing the project as a whole system instead of simply as a chain of independent tasks, allows for both shorter project lead times and enhanced reliability. But as I said befor, many project organizations are multiproject environments. How can TOC provide guidance for enhancing the ability of a multiproject organization to be more productive in the quantity of projects or new products undertaken and delivered?
Project and task times, due to focus and buffering, are shortened. Therefore, first we expect that the capacity hidden in and consumed by practices such as multi-tasking and task-based safety can be unleashed to simply do more work in the same timeframe. But even beyond that, the core of the TOC view of multiproject environments lies in recognizing that within a project organization, there is some resource that can be considered a bottleneck or constraint limiting the ability of the organization to do more projects. When we manage the individual projects using the TOC approach, the lack of multi-tasking and embedded safety makes it easier to ascertain the true capacity of project resources, and hence identify the constraint resource. Once the organization as a whole is managed with the constraint in mind, management attention becomes far more focused and decisions to further enhance project capacity are easier to justify and implement.
Shorter project lead times, improved reliability of project due dates, and increased capacity of the organization to take on more projects are not only predictable but have been observed in a number of organizations that have used this approach to projects in a variety of industries.
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Discuss Critical Chain - An email-based discussion group
Frequently Asked Questions about Critical Chain-based project Management
Top 10 Sources of Project Failure -- A list you probably won't see on Letterman.
Check Out the Following Links for More About the TOC Approach to Project Management:
Critical Chain and Risk Management - Protecting Project Value from Uncertainty -- Project management is the practice of turning uncertain events into certain promises. If so, then project management is an extended excersie in risk management. The core concepts underlying Critical Chain-based project management directly support risk management and are described in this paper, expanded from one presented at PMI's 2001 National Symposium.
Getting Out From Between Parkinson's Rock and Murphy's Hard Place -- This first link will bring up a paper based on a poster presentation originally given at the 1998 New Jersey PMI Chapter's annual symposium, honored with a "best of the show" award by attendees, and later turned into an article published in PMI's PM Network magazine.
Program Management -- Turning Many Projects into Few Priorities with TOC -- This link will lead to a paper on the key attributes of a TOC Multi-Project Management environment. (Most projects are performed by resources shared with other projects. It can be deadly to ignore the resulting interactions, no matter how well you manage single projects.) This paper was originally presented at PMI's Global Symposium in Philadelphia in October of 1999 and is included in the proceedings of that conference. Audio tapes of the presentation are also available from PMI.
Project Portfolio Management - The First Cut is the Kindest Cut - One of the common problems faced by project-oriented organizations is having too many projects relative to their capacity. Therefore, one of the first things that needs to be done is to determine what can be done is to determine what should be done . . . and what should not be done . . .
Consumption of Effort and Conservation of Energy for Project Success -- This link will lead to an essay on the necessity for managing protective capacity in multi-project environments to get the most organizational throughput from the efforts of project resources.
Critical Chain Basics
A Critical Chain Schedule
The Sooner You Start, The Later You Finish
Multitasking Multiplies Lead Time