Critical Path Method (CPM)

Photo by Bopuc
Photo by Bopuc

Photo by Bopuc

A visual network project planning tool very similar to PERT but activity centered instead of event-oriented. Because CPM can take cost into considerations it can be more rigorous than PERT.

  • Time and cost for each activity are considered.
  • Only items on the Critical Path are considered.
  • Duration is measured 2 ways.
    • Normal completion
    • Crash completion – i.e. if you throw money at it, can you complete it quicker.
      • If you “crash” an activity, a new Critical Path may be created.
  • Activities with the lower crash cost are selected first.
  • Critical path- longest path- slack time is 0.

ASQ Six Sigma Green Belt Critical Path Questions

Question:  The critical path for a project is best described as the:

(A) sequence of steps with the highest costs
(B) tasks in the project that have the highest risk of failure
(C) sum of the tasks with the shortest time requirements
(D) longest path from the start to the completion of the project

Answer: D – the longest path. This is a definition question for a critical path.

Float is the amount of time an activity may be delayed from its early start without delaying the project completion date.

◦Optimistic time – the shortest time in which the activity can be completed.
◦Most likely time – the completion time having the highest probability.
◦Pessimistic time – the longest time that an activity may take.

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