Thursday, October 17, 2013

Focus and Leverage Part 262

We said in an earlier posting that in the Critical Path (CPM) Method safety is imbedded within each task as a way to guard against the uncertainties of Murphy.  Critical Chain Project Management (CCPM) takes a completely different approach by assuming that Murphy’s uncertainty will happen in every project.  Unlike CPM, CCPM removes these safety buffers within each task and pools them at the end of the project plan to protect the only date that really matters, the project completion date.

There are many references that explain the details of how CCPM does this, but here’s a simple example to explain it.  That is, by simply removing all of the protection from individual task estimates which we have estimated to be 50 % of the original estimate.  Figure 6 demonstrates the removal of this safety.  So now, the length of the critical chain is no longer 34 days, but rather 17 days.  But instead of just eliminating the safety buffer, we want to place it where it will do the most good… the end of the project to protect the due date.  This isn’t exactly how this works, but for presentation purposes to demonstrate the theory behind CCPM it will suffice.

Figure 6
Figure 7 is this same process, but this time the safeties that we removed are added to the end of the project to act as a cushion to Murphy’s inevitable delays.  Actually, we have added only 50% of the time to create the project buffer.  So the question now becomes, how do we utilize this buffer and how does it improve the on-time completion of the project?

Figure 7
Suppose task A2 takes 7 days instead of the 5 days that are in the plan?  In a traditional project management environment, this would be cause for panic.  In a CCPM environment we simply consume two days from the project buffer and we’re still on schedule.  Suppose now, for task B3, we only take 3 days instead of the planned 5 days.  We simply add the gain of 2 days back into the project buffer. These actions are similar to a bank account with deposits and withdrawals.  When you need money, you withdraw it and when you have excess money, you deposit it.  In traditional CPPM, delays accumulate while any gains are lost.  This is a very significant difference!  The project buffer protects us from delays.  For non-critical chain tasks, or subordinate chains such as C1-C2 from our example, we also can add feeding buffers to assure that they are completed prior to negatively impacting/delaying the critical chain.  That is, in our example, as long as C2 is completed prior to D1, then the critical chain will not be delayed.

One of the key differences between CPM and CCPM is what happens at the task level.  In traditional project management we said earlier that each task has a scheduled start and completion date.  CCPM eliminates the times and dates from the schedule and instead focuses on passing on tasks as soon as they are completed.  This function serves to eliminate the negative effects of both the Student Syndrome and Parkinson’s Law from the equation and permits on-time and early finishes for projects.  In order for this to work effectively, there must be a way to alert the next resource to get ready in time.  This is equivalent to a relay race where the baton is handed off from one runner to the next.

Earlier, we explained that in traditional project management we track the progress of the project by calculating the percentage of individual tasks completed and then we compare that percentage against the due date or the percentage of remaining tasks.  The problem with this method is because we aren’t considering the estimated durations that are left to complete, it is nearly impossible to know exactly how much time is remaining to complete the project.  Using this method to track progress, many times you’ll see 90 % of a project completed relatively quickly only to see the remaining 10 % take just as long.  In fact, looking at the number or percentage of tasks completed instead of how much of the critical path has been completed, only serves to give a false sense of conformance to the schedule.

In my next posting we’ll look at the different way CCPM tracks the progress of projects and why it is simply a much better way of doing so.

Bob Sproull


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