Chapter 8: PERT, CPM, GERT

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Chapter 8 PERT, CPM, GERT
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PERT x CPM (both 1950s)

• Originated from Govern./Research
• (Navy/Lockheed)
• Focus on time
• Optimistic, most likely and pessimistic time

• Originated from private Industry
• Focus on cost
• Crash Time and Crash cost

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PERT Formulas p.231-232

• Optimistic, most likely, and pessimistic time
• Estimated time of task
• Estimate Variance of task
• Estimated time of project
• Estimated variance of project
• Z

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CPM

• Based on idea that a project has a Normal Time to
  complete a job. Normal time is the cheapest. If
  it takes longer or shorter, it will
• usually be more expensive.
• Why ?

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To crash a project , PM may need one or more of
the below, resulting in great cost

• Overtime workers
• Use breakthrough equipment
• Start a phase of the project (Design, for
  example) before a pre-requisite phase is
  completed (Analysis, for example)
• Hire consultants.

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Which Task to Crash ?

• Not a steep slope (big decrease in time with only
  little increase in cost)
• Task that is part of the CP.
• Crashing the task will not have a negative
  colateral result to the rest of the companys
  activities or projects (for example, need to stop
  something else to crash that task).

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GERT, different from others because

• Not all immediate predecessor activities must be
  completed before activity is started
• Looping back is permitted.
• Percentage probability

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Tasks not completed

• Q Example of a project where not all tasks need
  to be completed for the project to be completed ?
• A2 You research three different possible
  solutions to cure cancer (three different
  groups). Once one group solves the problem, other
  group (tasks) can be disactivated.
• A1 To decide if you give credit or not to
  somebody you do three types of credit check. If
  any two comes through with success, credit is
  conceived.

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