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Pert Estimating

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Basic information on how to create a task-level estimate

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Pert Estimating

  1. 1. PERT History <ul><li>The Program Evaluation and Review Technique commonly abbreviated PERT is a model for project management invented by Booz Allen Hamilton, Inc. under contract to the United States Department of Defense's US Navy Special Projects Office in 1958 as part of the Polaris mobile submarine-launched ballistic missile project. This project was a direct response to the Sputnik crisis. </li></ul><ul><li>PERT is basically a method to analyze the tasks involved in completing a given project, especially the time needed to complete each task, and identifying the minimum time needed to complete the total project. </li></ul><ul><li>PERT was developed in the 1950’s, primarily to simplify the planning and scheduling of large and complex projects. It was able to incorporate uncertainty by making it possible to schedule a project not knowing precisely the details and durations of all the activities. </li></ul>
  2. 2. Estimating Our Work Using PERT
  3. 3. Role of Estimating in Planning <ul><li>Planning is looking into the future </li></ul><ul><li>The future is uncertain </li></ul><ul><li>Thus, we cannot know (for sure) how much, how long, or how many </li></ul><ul><li>Sizing and Estimates allow us to plan despite this lack of knowledge </li></ul><ul><ul><li>Sizing is about getting into the right ballpark </li></ul></ul><ul><ul><li>Early estimates are about getting into the right section </li></ul></ul><ul><ul><li>Later estimates are about getting into the right seat </li></ul></ul><ul><li>See “Cone of Uncertainty” </li></ul>
  4. 4. This isn’t estimating <ul><li>“Don’t worry, we will just wing it” </li></ul><ul><li>“I remember last time -- it will be the same” </li></ul><ul><li>Just ask someone who has done it </li></ul>
  5. 5. More Empirical <ul><li>Historical data </li></ul><ul><li>Industry or company standards </li></ul><ul><li>Use of real experts with actual knowledge </li></ul>
  6. 6. Problem surrounding estimating <ul><li>No perfect foresight </li></ul><ul><li>History is never really repeated </li></ul><ul><li>The unforeseen usually does happen </li></ul><ul><li>“ Experts” do not agree </li></ul><ul><li>Poor memory </li></ul><ul><li>Projects without a history to rely upon </li></ul><ul><li>People are different </li></ul>
  7. 7. An Example to Study It is to be a wonderful warm spring Saturday, the first wonderful spring weekend of the year. Tomorrow will be a perfect day to get the yard mowed
  8. 8. Let’s see, what do we know <ul><li>½ acre of lawn </li></ul><ul><li>Self-propelled walking mower </li></ul><ul><li>Weather is great </li></ul><ul><li>Natasha wants us to take Felix to the lake for an afternoon family picnic </li></ul>
  9. 9. As you return from walking Fido Natasha asks a simple question 9 o’clock How long until you are available to drive to the lake? Oh, uh, . . . . 2 hours The trap has been set – you are already in trouble, Boris!!
  10. 10. What Should Go into a Good Estimate? <ul><li>An understanding of the work to be done </li></ul><ul><li>Problem decomposition </li></ul><ul><li>Careful thought surrounding what you do and do not know about the work pieces </li></ul><ul><li>Smart communication of the estimate </li></ul>
  11. 11. Boris’ Problem: He did not think about <ul><li>First mowing of the year </li></ul><ul><li>Mower is in the back of the ill-kept shed ! </li></ul><ul><li>Does he have gas; and oil ? </li></ul><ul><li>Mower was not serviced in the fall !!! </li></ul><ul><li>How long will the edging take ? </li></ul><ul><li>What about the “weed-whacking” ? </li></ul>Still think 2 hours ????
  12. 12. The other part of Boris’ problem 9 o’clock How long until you are available to drive to the lake? Oh, uh, 2 hours Good, I’ll have the kids ready to leave at 11 o’clock
  13. 13. <ul><li>Let’s look at a technique to keep Boris out of trouble </li></ul><ul><li>and us ! </li></ul>
  14. 14. The Development of PERT <ul><li>Program Evaluation and Review Technique </li></ul><ul><li>Major US Navy project of 1950s -- Polaris </li></ul><ul><li>Revolutionary advances in submarines, missiles and guidance systems </li></ul><ul><li>Historical information will be of little value </li></ul><ul><li>New estimating tool developed along with new PM methodology </li></ul>
  15. 15. Fundamental PERT Estimating Dilemma <ul><li>How to develop reasonable estimates </li></ul><ul><li>so we can </li></ul><ul><li>plan smartly </li></ul><ul><li>when we are short </li></ul><ul><li>on information about the problem to be solved? </li></ul>
  16. 16. The PERT Solution <ul><li>Take advantage of what you do have </li></ul><ul><li>Smartly hedge your response </li></ul><ul><li>Prepare to sense variations quickly </li></ul><ul><li>Be ready to respond when new information becomes available </li></ul>
  17. 17. PERT estimating formula <ul><li>Optimistic + 4 (Most Likely) + Pessimistic </li></ul><ul><li>Estimate = </li></ul><ul><li>6 </li></ul>
  18. 18. PERT is a 5-Input Model <ul><li>Most likely prediction </li></ul><ul><li>Pessimistic prediction </li></ul><ul><li>Reasons to anticipate better performance </li></ul><ul><li>Optimistic prediction </li></ul><ul><li>Reasons to anticipate poorer performance </li></ul>
  19. 19. What is needed when preparing an estimate? <ul><li>Clear description of the work </li></ul><ul><li>Understanding of the environment and tools you are going to use to solve the problem </li></ul><ul><li>A desire for self-preservation </li></ul><ul><ul><li>Willingness to think about the problem before attempting to solve the problem </li></ul></ul><ul><ul><li>Generally a poor estimate leads to underestimated the effort / time to complete the work </li></ul></ul><ul><ul><li>This leads to long hours to meet these estimates </li></ul></ul><ul><ul><li>At least this is what it means in IT </li></ul></ul>
  20. 20. NJM Worksheet Final Estimate Adjustment Logic:     hours TBD PERT calculated time:     hours Most likely time:     hours Pessimistic time:   Reasons for a slower time:   hours Optimistic time:   Assumptions Reasons for a quicker time: Activity/Task   Phase Logic and Adjustments Work to be Accomplished   Role: Individual: Project:   Project Work Estimating Sheet (PERT Methodology)
  21. 21. What is Boris’ Real Work <ul><li>Get the tools (mower, edger, whacker) out of the shed </li></ul><ul><li>Get the mower running </li></ul><ul><li>Actually cut the lawn </li></ul><ul><li>Edge the sidewalk and driveway </li></ul><ul><li>Weed-whack around the shrubs, mailbox and light pole </li></ul><ul><li>Put tools away </li></ul>
  22. 22. Discussion of the Groups’ Work
  23. 23. Make Your Future Easier <ul><li>The best estimates start with documented experience on similar tasks </li></ul><ul><li>This means we must do a good job of capturing actual time spent on current work </li></ul><ul><li>Diligence in using the time reporting function of PlanView will make our future estimating life easier </li></ul>
  24. 24. Questions