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34
Project Management
Planning the Time Dimension
When planning the time dimension, the objective is to
determine the shortest time necessary to complete the
project. Begin with the WBS and determine the time
necessary to complete each step or subunit. Next, determine
the sequence in which steps must be completed, and which
steps can be underway simultaneously. From this analysis,
you’ll determine the three most significant time elements:
X The duration of each step
X The earliest time at which a step may be started
X The latest time by which a step must be started
Planning the time dimension can be done only by people who have experience with
the activities designated for each step. If you personally don’t know how long it
takes to do something, you need to rely on someone who does have the requisite
experience.
Many project managers find it realistic to estimate time intervals as a range rather
than as a precise amount. Another way to deal with the lack of precision in
estimating time is to use a commonly accepted formula for a task. If you’re working
with a mathematical model, you can determine the probability of the work being
completed within the estimated time by calculating a standard deviation of the time
estimate.
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DO NOT ALTER OR DELETE THIS LINE – It is here for spacing purposes.
PLANNING THE TIME REQUIRED
When you’re involved with a project, how do you estimate the time required for
its completion?
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35
3: Planning the Project
Using a Mathematical Model to Estimate Time
T
m
The most probable amount of time necessary to complete the project.
T
o
—The optimistic (shortest) time, within which only 1% of similar projects are
completed.
T
p
—The pessimistic (longest) time, within which 99% of similar projects are
completed.
T
e
—The calculated time estimate.
T
o
+ 4T
m
+ T
p
T
e
=
6
ı = Standard deviation
T
p
- T
o
ı =
6
The work will be completed within the range of T
e
± 1 standard deviation or 68.26%
of the time.
The work will be completed within the range of T
e
± 2 standard deviations or
95.44% of the time.
The work will be completed within the range of T
e
± 3 standard deviations or
99.73% of the time.
With a duration set for each subunit, the next step is to determine the earliest and
latest times for starting each one. Gantt charts and PERT diagrams are two methods
commonly used to chart a project. Both are discussed in the pages that follow.
36
Project Management
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DO NOT ALTER OR DELETE THIS LINE – It is here for spacing purposes.
PRACTICE ESTIMATING TIME
For the same project that you’ve been using, determine a time estimate for each
of the project’s subunits or steps.
Subunit or Step T
o
T
p
T
m
T
e
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DO NOT ALTER OR DELETE THIS LINE – It is here for spacing purposes.

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