Critical Chain Presentation

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Introduction to Critical Chain
The Use of Buffers for Contingency
Sizing Tasks and Buffers
Simulating Buffers in Microsoft Project
Considerations When Using Critical Chain

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Critical Chain Presentation

  1. 1. Critical Chain as an Extension to CPM Orlando A. Moreno, PMP February 11, 2003 [email_address]
  2. 2. Overview <ul><li>Introduction to Critical Chain </li></ul><ul><li>The Use of Buffers for Contingency </li></ul><ul><li>Sizing Tasks and Buffers </li></ul><ul><li>Simulating Buffers in Microsoft Project </li></ul><ul><li>Considerations When Using Critical Chain </li></ul>Orlando Moreno 2/11/03 408.656.2498
  3. 3. Scheduling Issues Addressed by Critical Chain <ul><li>Inherent uncertainty in task duration estimates </li></ul><ul><li>Parkinson’s Law: </li></ul><ul><li>Work expands to fill the available time. </li></ul><ul><li>Student Syndrome: </li></ul><ul><li>Wait until the last minute to start a task. </li></ul>Orlando Moreno 2/11/03 408.656.2498
  4. 4. Critical Chain Approach to Scheduling <ul><li>Account for both resource and precedence dependencies </li></ul><ul><li>Set task duration for 50% probability of completing on time </li></ul><ul><li>Add contingency with strategically placed buffers </li></ul>Orlando Moreno 2/11/03 408.656.2498
  5. 5. A Simple Example Will Illustrate the Use of Buffers <ul><li>Subsystem A requires six tasks (1 - 6) </li></ul><ul><li>Subsystem B requires four tasks (7 - 10) </li></ul><ul><li>Integration and test task (11) </li></ul><ul><li>Subsystem A is on the critical path </li></ul>Orlando Moreno 2/11/03 408.656.2498
  6. 6. Network Diagram Orlando Moreno 2/11/03 408.656.2498
  7. 7. Critical Chain Adds Buffers <ul><li>Feeding Buffer Provides contingency to keep tasks not on the critical path off the critical path </li></ul><ul><li>Project Buffer Provides contingency for the entire project </li></ul><ul><li>Resource Buffer Provides a wakeup call to alert resources to be ready to work on critical tasks </li></ul>Orlando Moreno 2/11/03 408.656.2498
  8. 8. Network With Buffers Added Orlando Moreno 2/11/03 408.656.2498
  9. 9. Putting Feeding Buffers in All Paths Orlando Moreno 2/11/03 408.656.2498
  10. 10. Task Sizing <ul><li>Create three estimates </li></ul><ul><ul><li>Most Likely </li></ul></ul><ul><ul><li>Optimistic </li></ul></ul><ul><ul><li>Pessimistic </li></ul></ul><ul><li>Calculate mean </li></ul><ul><li>Use mean as an approximation for median </li></ul>Orlando Moreno 2/11/03 408.656.2498
  11. 11. Three Point Estimates with Mean Orlando Moreno 2/11/03 408.656.2498
  12. 12. Mean as a Reasonable Approximation to Median Orlando Moreno 2/11/03 408.656.2498
  13. 13. Buffer Sizing <ul><li>Contingency based on standard deviation of total path </li></ul><ul><li>Setting buffer to one standard deviation increases probability of completing on-time to 84% </li></ul>Orlando Moreno 2/11/03 408.656.2498
  14. 14. Example Path Calculations Orlando Moreno 2/11/03 408.656.2498
  15. 15. Simulating Buffers in Microsoft Project <ul><li>Add a task for the buffer at the end of the path </li></ul><ul><li>Add a milestone after the buffer </li></ul><ul><li>Set buffer duration based on calculations </li></ul>Orlando Moreno 2/11/03 408.656.2498
  16. 16. Simulating Buffers in Microsoft Project <ul><li>Constrain the task type of the milestone to: Must Finish On </li></ul><ul><li>Change the buffer to a milestone </li></ul><ul><li>Constrain the buffer task type to: As Soon As Possible . </li></ul><ul><li>The slack for the buffer will now be the buffer size </li></ul>Orlando Moreno 2/11/03 408.656.2498
  17. 17. Simulating Buffers in Microsoft Project Orlando Moreno 2/11/03 408.656.2498
  18. 18. Considerations When Using Critical Chain Orlando Moreno 2/11/03 408.656.2498
  19. 19. Statistical analysis assumes many tasks with small random variations <ul><li>Open ended tasks - the pessimistic estimate is significantly greater than the most likely - require special focus </li></ul><ul><ul><li>Identify and include in risk management plan </li></ul></ul><ul><ul><li>Consider changes to cost and scope to reduce uncertainty </li></ul></ul><ul><ul><li>Consider an iterative development strategy </li></ul></ul><ul><ul><li>Estimate range of possible completion dates </li></ul></ul>Orlando Moreno 2/11/03 408.656.2498
  20. 20. Statistical analysis assumes paths are not coupled <ul><li>Interim deliverables may be needed by other developers, </li></ul><ul><li>Multiple strongly coupled paths could impact the statistical calculations </li></ul><ul><li>Identify coupling and add to risk management plan </li></ul><ul><li>Consider Monte Carlo simulation when there is a high degree of coupling </li></ul>Orlando Moreno 2/11/03 408.656.2498
  21. 21. Getting the most benefit from 3-point estimates <ul><li>Create 3-point estimates in early top level schedule </li></ul><ul><li>Identify all assumptions about most likely, optimistic and pessimistic estimates </li></ul><ul><li>Assess cost and scope impact of these assumptions </li></ul><ul><li>Include most pessimistic completion estimate, cost and scope in all negotiations about schedule </li></ul>Orlando Moreno 2/11/03 408.656.2498
  22. 22. Questions Orlando Moreno [email_address] 408.656.2498 408.656.2498 [email_address]

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