Comparison of Two Buffer Management Methods in TOC Critical Chain Project Management (TOCPM / CCPM)
Sorry if you received this more than once. I am struggling through the idiosyncrasies of publishing on LinkedIn. I think I have it correct now.
I'm currently managing a small project ($1.2MM, 60 tasks, 242 days) using CCPM, and wanted to compare two different buffer management methods. If you don't use CCPM, then you won't understand "buffer management", but this post might get you interested if you are searching for better ways to keep commitments on your projects.
METHOD 1:?Buffer Management using "Decreasing Buffer Size" (DBS), as shown in Figure 2. This is the method I learned from Bob and Dee Jacob in 2005 at A. Goldratt Institute in 2005, the approach that has worked well for me on 60 - 70 CCPM / TOCPM projects since then. I believe that the use of DBS may be rare among CCPM practitioners. In DBS, the initial project buffer is sized as "50% of safety removed" from the Critical Chain, divided into equal GREEN, YELLOW and RED zones to signal the need to act for project recovery. Traditionally, the signal is interpreted as:
Figures 2 and 3 shows a unique feature of DBS. As we finish a task on the critical chain during project execution, we REDUCE the size of the project buffer by subtracting the days of safety the completed Critical Chain task contributed to the project buffer. As a result, the GREEN, YELLOW, RED action zones "shrink" toward the promise date at the top of the RED zone, since we no longer carry protection for tasks that have finished.
METHOD 2: Buffer Management using a traditional "Fever Chart", as shown in Figure 4. I believe that this is the method used by most CCPM practitioners on their projects. Again, the initial project buffer size is "50% of safety removed" from the critical chain. This buffer size is SUSTAINED throughout execution of the project. As shown in Figure 4, the project buffer is divided into GREEN, YELLOW and RED action zones according to standard Fever Chart rules.
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SO, WHAT IS THE POINT OF MY LITTLE STUDY?
The point is to compare the difference in ACTION SIGNALS for PROJECT RECOVERY, as provided by two buffer management methods; 1) "Decreasing Buffer Size" (DBS) and 2) "Traditional Fever Chart" (TFC). I thought some might be interested in the results of this study, which I will update from time to time.
Figure 5 below shows this difference in ACTION (project risk) SIGNALS, just 40 days into this 242-day project (195 workdays aggressive + project buffer of 47 workdays). So far, there is already a significant difference in ACTION SIGNALS from the two methods, as indicated by the big yellow arrows in Figure 5.
Using Method 1, DBS, the project has spent NO TIME so far in a YELLOW or RED risk status, indicating NO PROJECT RECOVERY ACTION to return the project status to GREEN. However, using buffer management Method 2, TFC, the figure shows that 17 of the first 40 days of the project have been spent in a YELLOW or RED risk status. This signals that the project team would have needed to plan or act for project RECOVERY during those occasions.
If Method 1 (DBS) gives a better ACTION SIGNAL for project recovery, then Method 2 (TFC) may sometimes be yielding a "Type 1 Error" in the action signal provided. This is analogous to a "false positive" during inspection or testing and may prompt the team “take action when no action is necessary”. This can waste precious project resources and time. Instead, buffer management Method 1, “Decreasing Buffer Size” could save time and decrease chaos for the PM, the project team and the project client.
I will continue to monitor this "experiment" and report again later in the project.