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USING PROJECT SCHEDULER 8 207

about 10 percent of the time. The third estimate is the most likely, which we are
now able to obtain without deliberate bias. The traditional PERT formula, for cal-
culating task durations, is (A + 4B + C) / 6, where A is the pessimistic, B is the
most likely, and C is the optimistic (the most likely is given a weight of four times
the optimistic and pessimistic). But there are other options, as we will soon see.

Other advantages are: (1) we gain a range of task and project durations, (2) we
can adjust weight factors to generate schedules with higher or lower confidence fac-
tors, and (3) we can evaluate the potential for achieving any selected project end
date. We also expand the capability for performing what-if analyses. We can use this
increased information about durations in our analyses of the schedule, whether per-
formed by simple observation or via computerized probability analysis.

It’s time to look at our three computer-based approaches to duration analysis.
In Chapter 6.2, we argue that traditional CPM schedules produce a project end
date calculation that could have a 50 percent or less possibility of being met.
These programs address this issue, in varying degrees of sophistication. They are
easy to understand, even if you are sigmaphobic. But ease-of-learning and ease-
of-use do increase with the level of sophistication. I don’t necessarily recommend
them for everyone or every project. But when meeting a schedule date is impor-
tant, and especially when there are dire consequences for missing schedule dead-
lines, these three programs will generate better estimates and an understanding
of the potential (or improved confidence) for achieving the end dates.

Using Project Scheduler 8

Example one features a general purpose CPM program that also offers support
for the three time estimate (PERT) approach. Several products have a PERT ca-
pability, but we will look at Project Scheduler 8, from Scitor, because of some of
its special PERT features.

In PS8, we can activate the PERT mode and add a PERT DUR column to the
task table. We can enter the three time estimates, and (in a special PS8 feature)
adjust the weighting factors. In Figure 6.3a, we can see that (using the traditional
1/4/1 weighting) the calculated project duration is 21.33 days (vs. the 20 days us-
ing the single estimates).

By adjusting the weight factors, we can calculate various degrees of optimism
or confidence. Using a 1/0/0 weighting, we calculate the project using only the
optimistic durations. In this case we can say that the best possible project end
date is 10/16 or 16 days. By changing to a 0/0/1 weighting (all pessimistic) we can
project a worst case of 11/1 or 32 days.

Another option is to deliberately add time contingency, by giving more weight
to the pessimistic dates. In the model above, setting the weight factors to 1/4/5