The Project Manager's Challenge
The problem facing the project manager is that on the one hand he or she wants
to manage both schedule and cost to realistic expectations (using either most
likely or weighted average estimates), and on the other hand wants a high degree
of certainty that he or she will complete the project within both schedule and
This is a challenge because a realistic estimate, at best, represents a 50:50
probability that one can deliver the project for the agreed upon cost and schedule,
or do better, as shown in Figure 3. In reality, because
of the nature of the statistical chances of being correct when making estimates,
our chances of completing the project on the favorable side of the estimate when
using most likely estimates are actually less than 50:50. As shown in the graph,
the "most likely" value has the greatest chance of being correct, but is still
Because of the skew of the estimating probability curve, Figure 3,
the weighted average drives the expected cost higher and duration longer.
If that is the case, what project manager wants to stake their reputation on delivering
less than half their projects on or below budget and/or on time or ahead of schedule?
Yet we still want to manage to realistic expectations.
Figure 3: Estimating Probability Curve
Contingency reserves, therefore, can be used to increase the probability
of completing the project within agreed-to targets to a higher confidence level.
For example, perhaps you would like to commit to a schedule and budget that you
are 80%, 90%, or even 95%, sure you will complete within targets, see Figure 4.This
assumes that the contingency reserve is incorporated into the performance
management baseline, which is the benchmark against which performance measurements
are taken and reported.
But on the other hand, what project manager wants his or her project team to
think that they have all this extra time and budget to work with, or management
to think he or she has padded the estimates? Does anyone doubt that if we make
the reserve amounts of time and budget visible that the team is likely to deliver
against the longer schedule and higher budget figure, even if no risks materialize
that require the allocation of these reserves? It is all too easy for project
team members to lose their sense of urgency to keep the project moving forward
and closely manage costs and time.
Figure 4: Impact of changing the odds