Project Time Management. Critical Path versus Critical Chain

Transcription

1 Project Time Management Critical Path versus Critical Chain

2 Goals for Today Understand how PMI does Project Time management Show what is missing in our Critical Path methodology Introduce you to Dr. Eliyahu Goldratt Developer of Theory of Constraints and Critical Chain Project Management Author and Philosopher Suggest a more complete way of running projects You will not leave today as an expert in Critical Chain but I hope it will peek your interest in learning more

3 Res Res The Iron Triangle of Project Management

4 This triangle fails to address All resources are NOT equal

5 Excerpt from The Project Management Body of Knowledge (PMBOK) 4 th edition The relationship between Critical Path, Critical Chain and Schedule Compression Develop Schedule: Tools and Technique Critical Path Methodology (CPM) Critical Chain Method Schedule Compression (Crashing and Fast Tracking)

6 Excerpts from PMBOK Schedule Compression Defined Schedule Compression Schedule compression shortens the project schedule without changing the project scope, to meet schedule constraints, imposed dates, or other schedule objectives. Schedule compression techniques include: Fast Tracking Crashing

7 Excerpts from PMBOK Schedule Compression Technique Fast tracking. A schedule compression technique in which phases or activities normally performed in sequence are performed in parallel. An example is constructing the foundation for a building before completing all of the architectural drawings. Fast tracking may result in rework and increased risk. Fast tracking only works if activities can be overlapped to shorten the duration.

8 Fast Tracking Technique Fast tracking. A schedule compression technique in which phases or activities normally performed in sequence are performed in parallel. An example is constructing the foundation for a building before completing all of the architectural drawings. Fast tracking may result in rework and increased risk. Fast tracking only works if activities can be overlapped to shorten the duration.

9 Fast Tracking Tradeoffs Rework could actually cause the schedule to be lengthened! Fast tracking. A schedule compression technique in which phases or Fast Tracking can only be used activities normally performed in sequence are performed in parallel. An example is constructing the foundation for a building before completing all of the architectural drawings. Fast tracking may result in rework and increased risk. Fast tracking only works if activities can be overlapped to shorten the duration. where activities can be overlapped Understand and manage the risks

10 Excerpts from PMBOK Schedule Compression Techniques Crashing. A schedule compression technique in which cost and schedule tradeoffs are analyzed to determine how to obtain the greatest amount of compression for the least incremental cost. Examples of crashing could include approving overtime, bringing in additional resources, or paying to expedite delivery to activities on the critical path. Crashing only works for activities where additional resources will shorten the duration. Crashing does not always produce a viable alternative and may result in increased risk and/or cost.

11 Crashing Techniques Crashing. A schedule compression technique in which cost and schedule tradeoffs are analyzed to determine how to obtain the greatest amount of compression for the least incremental cost. Examples of crashing could include approving overtime, bringing in additional resources, or paying to expedite delivery to activities on the critical path. Crashing only works for activities where additional resources will shorten the duration. Crashing does not always produce a viable alternative and may result in increased risk and/or cost.

12 Crashing Tradeoffs Crashing nearly always adds cost. Crashing. A schedule compression technique in which cost and schedule tradeoffs are analyzed to determine how to obtain the greatest Make sure your budget amount of compression for the least incremental cost. Examples of crashing can could handle include approving the added overtime, bringing in additional resources, or paying to expedite delivery to activities on the critical path. Crashing only works Expense! for activities where additional resources will shorten the duration. Crashing does not always produce a viable alternative and may result in increased risk and/or cost. Discuss this with your sponsor

13 Andy Crowe, PMP Crashing Crashing adds more resources to an activity. This usually increases the cost due to the law of diminishing returns which predicts that 10 people usually cannot complete an activity in half the time that 5 people can. The savings from crashing are rarely linear.

14 Why Crashing often doesn t work People are not all the same Different Skills Different work capacities Having More people is not always a solution In Fact it is rarely the solution It often takes more time Having the Right people is more important!

15 Critical Path Versus Critical Chain Major Difference Even though the Critical Path method is more popular than Critical Chain, Critical Path does not take resources into account where Critical Chain does

16 Project Time Management- Critical Path Method From the Project Management Body of Knowledge (PMBOK) Critical Path is generally, but not always, the sequence of schedule activities that determines the duration of the project. It is the longest path through the project. Critical Path Methodology (CPM) [Technique]. A schedule network analysis technique used to determine the amount of scheduling flexibility (the amount of float) on various logical network paths in the project schedule network, and to determine the minimum total project duration. Early start and finish dates are calculated by means of a forward pass, using a specified start date. Late start and finish dates are calculated by means of a backward pass, starting from a specified completion date, which sometimes is the project early finish date determined during the forward pass calculation.

17 Time Estimates How do we determine how long an activity will take? Expert Judgment Asking the most experienced person to judge the time This is often the person doing the work Could lead to a conflict of interest Historical Data Experience of the company doing this activity before More reliable, but limited

18 Problems with Estimating Time Most people do not want to be late so they normally pad the time estimate Experts estimate how long it would take them to do a specific task but the person who actually does that task may not have the same expertise Time estimates almost always end up being negotiated If you are negotiating with the person doing the work, who do you think is going to be right in the end?

19 PERT (Program/Project Evaluation and Review Technique) Developed in the 1950 s by the US Navy in conjunction with Booze, Allen and Hamilton Also Called 3-point estimate, Often used in Critical Path Methodology Start with 3 estimates: Pessimistic Realistic Optimistic The Formula for a 3-point estimate (or PERT) is: (Pessimistic + 4xRealistic + Optimistic)/6

20 Example of PERT Given: Optimistic 10 days Pessimistic 25 days Realistic 15 days (25 + 4x )/6= ( )/6= 95/6 = PERT works well but it is only as good as the estimates which were probably acquired through expert judgment. But, is a little bit more objective than Expert Judgment alone

21 The Delphi Technique An information gathering technique used as a way to reach consensus from experts Responses from the experts are anonymous Responses are summarized then re-distributed to the experts for comment Consensus may be reached in a few rounds of this process This technique helps reduce bias keeps any one person from having undue influence Drawbacks are that we need a more than one or two experts Takes more time that we typically want to spend estimating time

22 Critical Path Calculation The PMI Way Once duration is estimated for each activity build a table with each activities duration and dependencies Activity Duration Dependent on Start 0 A 3 Start B 4 Start C 2 Start D 2 B E 5 A,C F 1 B G 6 D, F H 11 E I 8 D, F Finish 0 G,H,I

23 Critical Path Calculation The PMI Way Draw a network diagram

24 The next step is to list out all of the paths through the network. The six paths are: Start-A-E-H -Finish Start-B-F-I-Finish Start-B-D-I-Finish Start-C-E-H -Finish Start-B-F-G-Finish Start-B-D-G-Finish

25 The last step is to add up all of the values associated with each path as is done below: Start-A-E-H-Finish = = 19 Start-C-E-H-Finish = = 18 Start-B-F-I-Finish = = 13 Start -B-F-G-Finish = = 11 Start-B-D-I-Finish = = 14 Start-B-D-G-Finish = = 12

26 Start-A-E-H-Finish = = 19 Start-C-E-H-Finish = = 18 Start-B-F-I-Finish = = 13 Start -B-F-G-Finish = = 11 Start-B-D-I-Finish = = 14 Start-B-D-G-Finish = = 12 The critical path emerges as Start-A-E-H-Finish because the path adds up to 19, which is longer than any of the other paths. If any of the activities in this path are delayed, the finish of the project will be delayed.

27 We are not done yet we now need to calculate Float or Slack time. Activity Duration Dependent on Start 0 A 3 Start B 4 Start C 2 Start D 2 B E 5 A,C F 1 B G 6 D, F H 11 E I 8 D, F Finish 0 G,H,I

28 Eliminate the critical path and subtract all paths from critical path Start-A-E-H -Finish Start-B-F-I-Finish Start-B-D-I-Finish Start-C-E-H -Finish Start-B-F-G-Finish Start-B-D-G-Finish

29 The Critical path ALWAYS has zero float Subtract each path from critical path Start-A-E-H-Finish = = 19 Start-C-E-H-Finish = = 18 Start-B-F-I-Finish = = 13 Start -B-F-G-Finish = = 11 Start-B-D-I-Finish = = 14 Start-B-D-G-Finish = = 12 Float 19-19= = = = = = 7

30 Each activity s float must also be calculated to get a full picture To accomplish this we need to do a Forward Pass and a Backward Pass

31 Use a Forward Pass to calculate Early Start and Early Finish

32 Do a Backward Pass to calculate Late Start and Late Finish Times

33 Now we have both Early and Late Start and Finish Times

34 For Critical Path Early and Late times are the same No Float

35 To Calculate Float subtract Early Start from Late Start OR Early Finish from Late Finish = = =

36 Why would anyone go through this when Microsoft Project will calculate your critical path for you Critical Path is in Red

37 Microsoft Project will also draw your network diagram for you Critical path is in Red

38 What is missing from our Plan? We have not accounted for our Resources

39 Critical Path drives bad behavior Student syndrome Starting work only as the deadline approaches, not right away when assigned Parkinson s Law Work expands so as to fill the time available for its completion

40 More bad behavior due to Critical Path The confidence gap I m confident I can drive to work in 20 minutes, but if I factor in the unexpected (snow storm, auto accident) I d have to say >1 hour All delays are passed on to the next task, early completions are rarely passed on to the next task as there is no incentive to do so If a resource knows they have extra time they will probably try to multitask

41 The Science of Multitasking A study in the Journal of Experimental Psychology: Human Perception and Performance (Vol. 27, No. 4) indicates that multitasking may actually be less efficient--especially for complicated or unfamiliar tasks--because it takes extra time to shift mental gears every time a person switches between the two tasks.

42 The Science of Multitasking Excerpts from American Psychological Association (American Psychological Association, March 20, 2006) Doing more than one task at a time, especially more than one complex task, takes a toll on productivity. Thus, multitasking may seem efficient on the surface but may actually take more time in the end and involve more error. even brief mental blocks created by shifting between tasks can cost as much as 40 percent of someone's productive time. Understanding the hidden costs of multitasking may help people to choose strategies that boost their efficiency - above all, by avoiding multitasking, especially with complex tasks.

43 Getting back to our Project This is a small software project Only last 19 days Only needs 2 programmers All programmers are the same right? Programmers Fred Joe Activity Duration Dependent on Resource Name Start 0 A 3 Start Fred B 4 Start Joe C 2 Start Fred D 2 B Joe E 5 A,C Fred F 1 B Joe G 6 D, F Fred H 11 E Joe I 8 D, F Fred Finish 0 G,H,I Joe

44 Adding Resources to our project yields this But this is not a problem, MS project will take care of this, just press the resource leveling button Notice the little red people this indicates a resource issue

45 Asking MS Project to level resources yields this MS Project s answer to this dilemma is just to push out the end date from 11/15 to 11/22 Our Critical path has also changed from AEH to BFG

46 Results of resource leveling Our project end date moved Our critical path is now different Our project is now going to be 4 days late On a project that was only 19 days to begin with this is a slippage of 29% Customer isn t happy Sponsor isn t happy

47 Critical Chain The answer is to account for resources before we commit to our schedule

48 Project Time Management- Critical Chain Method From the Project Management Body of Knowledge (PMBOK) Critical Chain Method Critical chain is a schedule network analysis technique that modifies the project schedule to account for limited resources. Initially, the project schedule network diagram is built using duration estimates with required dependencies and defined constraints as inputs. The critical path is then calculated. After the critical path is identified, resource availability is entered and the resource-limited schedule result is determined. The resulting schedule often has an altered critical path. The resource-constrained critical path is known as the critical chain. The critical chain method adds duration buffers that are non-work schedule activities to manage uncertainty. One buffer, placed at the end of the critical chain, is known as the project buffer and protects the target finish date from slippage along the critical chain. Additional buffers, known as feeding buffers, are placed at each point that a chain of dependent tasks not on the critical chain feeds into the critical chain. Feeding buffers thus protect the critical chain from slippage along the feeding chains. The size of each buffer should account for the uncertainty in the duration of the chain of dependent tasks leading up to that buffer. Once the buffer schedule activities are determined, the planned activities are scheduled to their latest possible planned start and finish dates. Consequently, in lieu of managing the total float of network paths, the critical chain method focuses on managing remaining buffer durations against the remaining durations of task chains.

49 The resource-constrained critical path is known as the critical chain. The critical chain method adds duration buffers that are non-work schedule activities to manage uncertainty. One buffer, placed at the end of the critical chain, is known as the project buffer and protects the target finish date from slippage along the critical chain. Additional buffers, known as feeding buffers, are placed at each point that a chain of dependent tasks not on the critical chain feeds into the critical chain. Feeding buffers thus protect the critical chain from slippage along the feeding chains. The size of each buffer should account for the uncertainty in the duration of the chain of dependent tasks leading up to that buffer. Once the buffer schedule activities are determined, the planned activities are scheduled to their latest possible planned start and finish dates. Consequently, in lieu of managing the total float of network paths, the critical chain method focuses on managing remaining buffer durations against the remaining durations of task chains. Project Time Management- Critical Chain Method From the Project Management Body of Knowledge (PMBOK) Critical Chain Method Critical chain is a schedule network analysis technique that modifies the project schedule to account for limited resources. Initially, the project schedule network diagram is built using duration estimates with required dependencies and defined constraints as inputs. The critical path is then calculated. After the critical path is identified, resource availability is entered and the resource-limited schedule result is determined. The resulting schedule often has an altered critical path.

50 Critical Chain Method from Wikipedia Critical chain project management (CCPM) is a method of planning and managing projects that puts the main emphasis on the resources required to execute project tasks. It was developed by Dr. Eliyahu M. Goldratt. This is in contrast to the more traditional critical path and PERT methods, which emphasize task order and rigid scheduling.

51 Critical Chain Method from Wikipedia (continued) A Critical Chain project network will tend to keep the resources levelly loaded, but will require them to be flexible in their start times and to quickly switch between tasks and task chains to keep the whole project on schedule. Application of CCPM has been credited with achieving projects 10% to 50% faster and/or cheaper than the traditional methods (i.e. CPM, PERT, Gantt, etc.) developed from 1910 to 1950s

52 Why do Critical Chain? From Wikipedia: Application of CCPM has been credited with achieving projects 10% to 50% faster and/or cheaper than the traditional methods According to Prochain Solutions: Improves speed by 30% Improves Predictability by more than 90% Increases Productivity Reduces: Stress, Errors and Wasted Time

53 Dr. Eliyahu Moshe Goldratt March 31, June 11, 2011 Israeli physicist who became a business management guru Best known for his Theory of Constraints (TOC) Critical Chain Project Management (CCPM) was derived from TOC Bestselling Author The Goal, It s Not Luck, Beyond the Goal, Critical Chain, and others Great Philosopher

54 Eli Goldratt s Grave One, people are good. Two, every conflict can be removed. Three, every situation, no matter how complex it initially looks, is exceedingly simple. Four, every situation can be substantially improved; even the sky is not the limit. Five, every person can reach a full life. Six, there is always a winwin solution

55 Eli Goldratt Quotes People are good Stupidity has no limitations Common sense is not common at all Isn t it obvious? The more complex the problem, the simpler the solution must be

56 More Eli Goldratt Quotes Don t bark if you cannot bite As long as you cannot verbalize your intuition the only thing you will communicate is your own confusion If you think you can counter emotion with logic, you ve not been married

57 Get to Know Eli Goldratt Eli Goldratt video on Project Management

58 The Mechanics of Critical Chain S T A R T A E H C F I B D G F I N I S H Our network diagram redrawn to relative scale

59 The Mechanics of Critical Chain S T A R T A E H C F I B D G F I N I S H Start by cutting all Durations in half!

60 The Mechanics of Critical Chain S T A R T A E H C F I B D G F I N I S H All that slashed duration becomes the Project Buffer (yellow) which we put at the end of the project

61 The Mechanics of Critical Chain S T A R T A E H C F I B D G Project Buffer F I N I S H The new schedule looks like this

62 The Mechanics of Critical Chain S T A R T A E H C F I B D G Project Buffer F I N I S H Now we can add some small buffers called Feeder Buffers if necessary to protect the critical path These will come out of our project buffer

63 S T A R T This will not make you the most A E H popular person C F I Project Buffer B D G F I N I S H Explain that they will not be held to the due date, just get the work done as quickly as possible

64 The Project Manager owns and manages the buffer The buffer exists to protect the customer Ideally the buffer should be used at the same rate as the project is completed

65 Project Fever Chart Used to track the project Buffer Red- needs management attention Yellow- All is well Green- Ahead of schedule

66 Advantages of Critical Chain Resources can get to work as soon as possible and work as quickly as possible No reason to put the work off, there is nothing else to do No need to multitask they are only expected to deliver one thing at a time No reason to make the work fill a specified amount of time Team members should think of this as a relay race, not a marathon Go as quickly as possible on each leg they own Pass it to another team member as quickly as possible

67 This Change will Take Time People will reject this change They won t like their time cut in half They won t believe the system will work and may sabotage it It will require upper management support to be successful Sell them first! Warn them there will be complaints This requires a complete culture change Deliver on your improvement of schedule or cost and everyone will be sold on Critical Chain!

68 Resources to find out more about Critical Chain Eli Goldratt s Website Lots of information and many Free Videos Many videos on youtube Good Overview of Critical Chain Explanation from Dr. Lisa Lang, from More in-depth explanation of Critical Chain From Pro Chain Solutions

69 Questions?

70 Thank You Gary Terrell, PMP