2 Critical Path Method (CPM) CPM is a network diagramming technique used to predict total project durationA critical path for a project is the series of activities that determines the earliest time by which the project can be completedThe critical path is the longest path through the network diagram and has the least amount of slack or floatSlack or float is the amount of time an activity may be delayed without delaying a succeeding activity or the project finish date
3 Critical Path Method (CPM) There are normally several tasks done in parallel on a projectMost projects have multiple paths on the network diagramThe longest path or the path containing the critical tasks is deriving the completion dates for a projectYou are not finished with the project until you have completed all the tasks
4 Calculating the Critical Path First develop a good network diagram, which in turn requires a good activity list based on the WBS.Estimate the duration of each activityAdd the duration estimates for all activities on each path through the network diagramThe longest path is the critical path
5 Calculating the Critical Path (Cont’d) What does critical path really mean?The critical path shows the shortest time in which a project can be completed.If one or more of the activities on the critical path takes longer than planned, the whole project schedule will slip unless the project manager takes corrective action
7 More on the Critical Path A project team at Apple computer put a stuffed gorilla on the top of the cubicle of the person currently managing critical taskThis would let others know that the person under the pressure don’t need to be disturbed or distracted.The critical path is not the one with all the critical activities; it only accounts for timeThere can be more than one critical path if the lengths of two or more paths are the sameIn case of more than one critical path the project managers should keep track of all those critical pathsThe critical path can change as the project progresses.
8 How Critical Paths Change ,Suppose activities A,B,C,D,E,F and G all start and finish as plannedAssume that activity I runs into problems and takes more than 4 days to completeThis would make path C,G,I,J be longer than other pathsHence C,G,I,J would now be the Critical Path.
9 Using Critical Path Analysis to Make Schedule Trade-offs It is important to know what the critical path is throughout the life of a project. So the project manager can make tradeoffsBehind schedule tasks on the critical path need to be addressed by answering these questionsShould the schedule be renegotiated?Should more resources be allocated on other items on the critical path to make up for lost time?Is it ok if the project finishes behind schedule?Project team can proactively manage schedule using the critical path analysis.
10 Using Critical Path Analysis to Make Schedule Trade-offs Project Manager can use a technique to make tradeoffs. This technique involves determining the followingFree slack or free float is the amount of time an activity can be delayed without delaying the early start of any immediately following activitiesTotal slack or total float is the amount of time an activity may be delayed from its early start without delaying the planned project finish dateEarly Start Date is the earliest possible time an activity can start based on the project network logic.
11 Using Critical Path Analysis to Make Schedule Trade-offs Project Managers calculate free or total slack by conducting a forward pass or backward pass on the network diagramA forward pass through the network diagram determines the early start and finish datesA backward pass determines the late start and finish dates
12 Example of Forward Pass Tasks D and E precedes task HEarly start date for task H would be early finish date of task E. As it’s greater than early finish date of task D
13 Calculating Early and Late Start and Finish Dates B,C is critical path with no float or slackTask A has 5 days of free and total float or slack
15 How to Find the Critical Path General Foundry’s network with expected activity timesA 2C 2H 2E 4B 3D 4G 5F 3StartFinish
16 How to Find the Critical Path To find the critical path, need to determine the following quantities for each activity in the networkEarliest start time (ES): the earliest time an activity can begin without violation of immediate predecessor requirementsEarliest finish time (EF): the earliest time at which an activity can endLatest start time (LS): the latest time an activity can begin without delaying the entire projectLatest finish time (LF): the latest time an activity can end without delaying the entire project
17 How to Find the Critical Path In the nodes, the activity time and the early and late start and finish times are represented in the following mannerACTIVITY tES EFLS LFEarliest times are computed asEarliest finish time = Earliest start time + Expected activity timeEF = ES + tEarliest start = Largest of the earliest finish times of immediate predecessorsES = Largest EF of immediate predecessors
18 How to Find the Critical Path At the start of the project we set the time to zeroThus ES = 0 for both A and BStartA t = 2ES = 0 EF = = 2B t = 3ES = 0 EF = = 3
19 How to Find the Critical Path General Foundry’s ES and EF timesA 20 2C 22 4H 213 15E 44 8B 30 3D 43 7G 58 13F 34 7StartFinishFigure 13.4
20 How to Find the Critical Path Latest times are computed asLatest start time = Latest finish time – Expected activity timeLS = LF – tLatest finish time = Smallest of latest start times for following activitiesLF = Smallest LS of following activitiesFor activity HLS = LF – t = 15 – 2 = 13 weeks
21 How to Find the Critical Path General Foundry’s LS and LF timesA 20 2C 22 4H 213 15E 44 8B 30 31 4D 43 7G 58 13F 34 710 13StartFinishFigure 13.5
22 How to Find the Critical Path Once ES, LS, EF, and LF have been determined, it is a simple matter to find the amount of slack time that each activity hasSlack = LS – ES, or Slack = LF – EFFrom Table 13.3 we see activities A, C, E, G, and H have no slack timeThese are called critical activities and they are said to be on the critical pathThe total project completion time is 15 weeksIndustrial managers call this a boundary timetable
23 How to Find the Critical Path General Foundry’s schedule and slack timesACTIVITYEARLIEST START, ESEARLIEST FINISH, EFLATEST START, LSLATEST FINISH, LFSLACK, LS – ESON CRITICAL PATH?A2YesB314NoCD78EF10136GH15Table 13.3
24 How to Find the Critical Path General Foundry’s critical pathA 20 2C 22 4H 213 15E 44 8B 30 31 4D 43 7G 58 13F 34 710 13StartFinishFigure 13.6
25 Using the Critical Path to Shorten a Project Schedule Three main techniques for shortening schedules for activities on the critical path.Shortening durations of critical activities/tasks by adding more resources or changing their scopeCrashing is a technique used to decrease the duration of the project by assigning additional resources to tasks and decreasing the duration required for those tasks. Main disadvantage?Fast tracking activities by doing them in parallel or overlapping them. Main disadvantage?
26 Importance of Updating Critical Path Data It is important to update project schedule information to meet time goals for a projectThe critical path may change as you enter actual start and finish datesIf you know the project completion date will slip, negotiate with the project sponsor
27 Critical Chain Scheduling A method of scheduling that considers limited resources when creating a project schedule and includes buffers to protect the project completion dateUses the Theory of Constraints (TOC)This theory says that at any given time the project has an aspect or constraint which limits its ability to achieve more of its goals.For the system to attain any significant improvements the constraint might be identified and the whole system must be managed with it in mind
28 Critical Chain Scheduling The important thing is availability of scarce resources like people, software or hardware.Attempts to minimize multitaskingWhen a resource works on more than one task at a timeMultitasking can delay task completionIt can some times increase total duration like wasted setup time
30 Buffers and Critical Chain A buffer is additional time to complete a taskMurphy’s Law states that if something can go wrong, it will, like fears about estimates being reduced from sponsor side.Parkinson’s Law states that work expands to fill the time allowedIn traditional estimates, people often add a buffer to each task and use it if it’s needed or notCritical chain scheduling removes buffers from individual tasks and instead creates:Project buffers or additional time added before the project’s due dateFeeding buffers or additional time added before tasks on the critical path
32 Program Evaluation and Review Technique (PERT) PERT is a network analysis technique used to estimate project duration when there is a high degree of uncertainty about the individual activity duration estimatesPERT uses probabilistic time estimatesDuration estimates based on using optimistic, most likely, and pessimistic estimates of activity durations, or a three-point estimateThe main disadvantage is more work required than CPM
33 PERT Formula and Example PERT weighted average =optimistic time + 4X most likely time + pessimistic time6Example:8 workdays + 4 X 10 workdays + 24 workdays = 12 days 6where optimistic time = 8 daysmost likely time = 10 days, andpessimistic time = 24 daysTherefore, you’d use 12 days on the network diagram instead of 10 when using PERT for the above example
34 Schedule ControlThe final process in project time management is schedule controlLike scope control the schedule control is a portion of integrated change control process under the project integration managementThe goal of schedule control is to know the status of the schedule, influence the factors causing schedule changes, determine schedule changes and manage changes when they occur
35 Schedule Control Suggestions Perform reality checks on schedulesAllow for contingenciesDon’t plan for everyone to work at 100% capacity all the timeHold progress meetings with stakeholders and be clear and honest in communicating schedule issues
36 Controlling the Schedule It is important to address conflicts and allow management insight if any thing gets out of handProject managers must use discipline to control schedule like setting firm dates for key milestones and emphasizing the need to follow themTools and techniques include:Progress reportsA schedule change control systemProject management software, including schedule comparison charts like the tracking Gantt chartVariance analysis, such as analyzing float or slackPerformance management, such as earned value (Chapter 7)
37 Reality Checks on Scheduling First review the draft schedule or estimated completion date in the project charterPrepare a more detailed schedule with the project teamMake sure the schedule is realistic and followedAlert top management well in advance if there are schedule problems
38 Working with People Issues Strong leadership helps projects succeed more than good PERT chartsProject managers should use:EmpowermentIncentivesDisciplineNegotiation
39 Using Software to Assist in Time Management Software for facilitating communications helps people exchange schedule-related information in the form of Network diagrams with critical paths information, Gantt charts etcDecision support systems help analyze trade-offs that can be madeProject management software can help in various time management areas
40 Words of Caution on Using Project Management Software Many people misuse project management software because they don’t understand important concepts behind creating a network diagram, evaluating critical path or setting a schedule baselineYou must enter dependencies to have dates adjust automatically and to determine the critical pathYou must enter actual schedule information to compare planned and actual progress
41 Assignment # 1 Make a team of up to 3 people Select a Software Project of your own choiceDevelop Project Charter of the selected projectDeadline of this deliverable is