Earlier we demonstrated how by simply
eliminating multi-tasking, significant gains can be made in project completion
rates, but we still have to address the impact of the Student Syndrome and
Parkinson’s Law. We know that both of these behaviors work to lengthen the time
required to complete projects. Remember how excess safety is imbedded into
traditional project management plans? Resources estimate task times and add in
their own protection against disruptions caused primarily by Murphy. Knowing
that this safety exists, resources then delay starting work on their tasks
until the due date is close. Even if the resources don’t delay the task starts
and finish early, these early finishes are not reported and passed on. So how
does CCPM deal with these two behaviors?
While CPM relies on individual task durations
as well as scheduled start and completion dates, CCPM does not. The focus is no
longer on finishing individual tasks on time, but rather starting and
completing these tasks as soon as possible. So how does this work? Like CPM,
CCPM still gathers estimates on individual tasks and identifies its own version
of the Critical Path. Unlike CPM, CCPM considers competing resources (i.e. the
same resource has to work on different tasks) and makes them a part of the
critical path. Let’s look at an example of how CPM and CCPM identifies the
critical path.
CPM defines the critical path as the longest path of dependent tasks within a project. That is, tasks are dependent when the completion of one tasks isn’t possible until completion of a preceding task. The critical path is important because any delay on the critical path will delay the project correspondingly. The figure below is an example of a series of tasks which must be completed in a project with the critical path highlighted in grey. Traditional project management determines the critical path by looking at the task dependencies within the project. Task A2 can only be initiated after A1 is completed. Task B3 can only be performed after completion of B2 and C2 only after C1. Task D1 can only be performed after completion of A2, B3 and C2. Using CPM the critical path would have been identified as C1-C2-D1 and the project completion estimate would have been 29 days (i.e. 8d+12d+9d).
In addition to task dependencies there are
also resource dependencies that CPM fails to recognize. What if, in our
example, tasks A2 and B3 are performed by the same resource? Is the critical
path different? In the figure below we see the new critical path that includes a
provision for resource dependencies and as you can see the new critical path is
5d+10d+10d+9d or 34 days. So the minimum time to complete this project is now
34 days. In our opinion, the failure to consider resource dependencies is one
of the key reasons why project completion rates are so terrible. The simple
implication of incorrectly identifying the critical path, which we will now
refer to as critical chain, is the project team will never be able to complete
their project on time without heroic efforts, adding additional resources,
overtime or a combination of all three. The practical implication of
incorrectly identifying the real critical chain is that the focus will be on
the wrong tasks. Is this any different than focusing on non-constraints in our
earlier discussion on TOC?
We said earlier that safety is imbedded within
each task as a way to guard against the uncertainties of Murphy. Critical Chain
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. Basically we have removed all of the protection from
individual task estimates which we estimate to be 50 % of the original
estimate. The figure below 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…..at 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.
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. In traditional CPM, delays accumulate while
any gains are lost. This is a 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.
One of the key differences between CPM and
CCPM is what happens at the task level. In traditional project management 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, much like a runner in a relay race passing the baton. 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.
In my next blog posting, we’ll discuss how
Goldratt’s 5 Focusing Steps apply to project management and how we track
progress on both CPM and CCPM to demonstrate why CCPM offers a much more
reasonable way to do so.