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![Estimating with PERT
• PERT Formula (Expected Duration)
– =(P+4M+O)/6
• Standard Deviation = (P-O)/6
• Variance = [(P-O)/6]2
Task O
Optimistic
M
Most Likely
P
Pessimistic
PERT
(Expected
Duration)
Std Dev Variance
A 2
days
4
days
8
days
4.3
days
1
day
1
day](https://image.slidesharecdn.com/8-180307064516/75/08-Project-Time-Management-Upload-49-2048.jpg)
Uploaded byBhuWan Khadka
08. Project Time Management Upload
The document discusses project time management, emphasizing the importance of creating and scheduling a detailed activity list using various inputs such as scope statements, historical information, and expert judgment. It explains network scheduling techniques like PERT and CPM, including critical path determination, which identifies activities that directly affect project completion. Additionally, the document covers concepts like slack, lag, and various methods of schedule control to enhance project management efficiency.
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08. Project Time Management Upload
- 1.
- 2. An old jokewhen it comes to project time management “The first 90 percent of a project schedule takes 90 percent of the time. The last 10 percent takes the other 90 percent of the time.”
- 3. Components of projecttime management
- 4. Creating activity list •Creating the activity list relies on several completed documents, knowledge, and actions. Uses the following as inputs to the process: • WBS • Scope statement (description of the required work, and only the required work, to complete the project) • Historical information • Constraints ( deadline, cost) • Assumptions ( resources availability, weather condition) • Expert judgment
- 5. Mapping the activities •Once the activity list has been created, the activities must be arranged in a logical sequence • This process calls on the project manager and the project team to identify the logical relationships between activities In practice: “Sticky notes” can help sequence events. Put your activities on sticky notes and then plot them out on a white board. Draw arrows to show the relationship between activities. Want to make a change? It’s easy to rearrange the notes and the relationships
- 6. Scheduling • Schedule isthe conversion of a project action plan into an operating timetable • Basis for monitoring a project • One of the major project management tools • Work changes daily, so a detailed plan is essential • Not all project activities need to be scheduled at the same level of detail
- 7. Scheduling • Most ofthe scheduling is at the WBS level, not the work package level • Only the most critical work packages may be shown on the schedule • Most of the scheduling is based on network drawings
- 8. The project network Aflow chart that graphically depicts the sequence, interdependencies, and start and finish times of the project job plan of activities • Provides the basis for scheduling labor and equipment • Enhances communication among project participants • Provides an estimate of the project’s duration • Provides a basis for budgeting cash flow • Highlights “critical” activities and that can not be delayed • Help managers get and stay on plan
- 9. Network scheduling advantage •Consistent framework • Shows interdependences • Shows when resources are needed • Ensures proper communication • Determines expected completion date • Identifies critical activities
- 10. Network scheduling advantage •Shows which of the activities can be delayed • Determines start dates • Shows which task must be coordinated • Shows which task can be run parallel • Relieves some conflict • Allows probabilistic estimates
- 11. Network scheduling techniques: PERTand CPM • The program evaluation and review technique (PERT), was developed for the Polaris missile/submarine project in 1958 • Critical path method (CPM), developed by DuPont during the same time
- 12. Terminology • Activity: anelement of the project that requires time • Merge activity: an activity that has two or more preceding activities on which it depends • Parallel activities: activities that can occur independently and, if desired, not at the same time • Sequential activities: one activity must be completed before the next one can begin A C DB
- 13. Terminology • Immediate predecessor:an activity that must be completed just before a particular activity can begin • Event: the result of completing one or more activities • Network: the combination of all activities and events that define a project • drawn left-to-right • connections represent predecessors • Path: a series of connected activities • Critical: an activity, event, or path which, if delayed, will delay the completion of the project
- 14. Terminology • Critical path:the path through the project where, if any activity is delayed, the project is delayed • There is always a critical path • There can be more than one critical path • Burst activity: an activity that has more than one activity immediately following it (more than one dependency arrow flowing from it) B D A C
- 15. Terminology • Activity onArrow - Arrows represent activities while nodes stand for events • Activity on Node - Nodes stand for events and arrows show precedence
- 16. AON and AOAFormat Activity network, AON format Activity network, AOA format
- 17. Constructing the network •Begin with START activity • Add activities without precedences as nodes • There will always be one • May be more • Add activities that have those activities as precedences • Continue
- 18. Constructing the criticalpath • Forward pass – an additive move through the network from start to finish • Backward pass – a subtractive move through the network from finish to start • Critical path – the longest path from end to end which determines the shortest project length
- 19. Rules for forward/backwardpass Forward Pass Rules (ES & EF) • ES + Duration = EF • EF of predecessor = ES of successor • Largest preceding EF at a merge point becomes ES for successor Backward Pass Rules (LS & LF) • LF – Duration = LS • LS of successor = LF of predecessor • Smallest succeeding LS at a burst point becomes LF for predecessor
- 20. Node labels Early startID number Early finish Activity float Activity descriptor Late start Activity duration Late finish
- 21. Duration estimation methods •Past experience • Expert opinion • Mathematical derivation – Beta distribution • Most likely (m) • Most pessimistic (b) • Most optimistic (a) TE: Estimated time for activity σ: variance for activity duration
- 22.
- 23.
- 24. Calculating activity times () ( ) 2 2 2 6 6 4 σσ σ = − = ++ = ab bma TE
- 25.
- 26. Critical path andtime AON network, showing activation duration and variance
- 27.
- 28. Critical path andtime AON network, showing earliest and latest start and finish times, and critical path The longest of the paths through the network is a-d-j using 43 days, which means that 43 days is the shortest time in which the entire network can be completed. This is called the critical time of the network, and a-d-j is the critical path, usually shown as a heavy line
- 29. Slack • Free slack(or Float) • Is the amount of time an activity can be delayed after the start of a longer parallel activity or activities • Is how long an activity can exceed its early finish date without affecting early start dates of any successor(s) • Allows flexibility in scheduling scarce resources • Sensitivity • The likelihood the original critical path(s) will change once the project is initiated
- 30.
- 31. Slack The project hasa critical time of 43 days. Activity i must be finished by day 43. Also activity i requires 18 days to be accomplished. i must be started not later than day 25 ( 43- 18 = 25) if the project is to be complete on day 43. Because i cannot begin until activities g and h have finished, the latest time (LF) for each of these is also day 25.
- 32. Slack The difference betweenthe LS and the ES for an activity is called its float or slack. In the case of activity i, it must be started no later than day 25, but could be started as early as day 24, so it has one day of slack. It should be immediately obvious that all activities on the critical path have zero slack. Zero slack activities cannot be delayed without making the
- 33. Slack Another example, consider activityf. Its ES is day 20, which is equal to the EF of its predecessor activity b. The LS for activity f is 43 -14=29. If f is started later than day 29, it will delay the entire project. Activity f has slack of LS – ES = 29 – 20 = 9 days To find the slack for any activity, we make a backward pass (right to left) through the network just as we made a forward pass (left to right) to find the critical path and time
- 34.
- 35. Precedence diagramming • Finishto start • Start to start • Finish to finish • Start to finish
- 36. Precedence diagramming • Finishto start • Start to start • Finish to finish • Start to finishFinish-to-start (FS): Task A must complete before Task B can begin. Example: The foundation must be set before the framing can begin. Start-to-start (SS): Task A must start before Task B can start. Example: A crew of painters is painting a house. Task A is to scrape the flecking paint off the house and Task B is to prime the house. The workers scraping the house must start before the other workers can begin priming the house. All of the scraping doesn’t Finish-to-finish (FF) : Task A must complete before Task B does. Ideally, two tasks must finish at exactly the same time. Start-to-finish (SF): It requires that Task A start so that Task B may finish. Maybe encountered in construction and manufacturing.
- 37. Chances of meetingthe deadline
- 38. Assignment: • Consider thefollowing project ( time given in days) Calculate: 1. The network. 2. All expected activity times, variances, and slacks. 3. The critical path and expected completion time. 4. The probability the project will be done in 23 days.
- 40. More on ProjectTime Management
- 41. How Do WeManage Time? • Six processes – Define Activities – Sequence Activities – Estimate Activity Resources – Estimate Activity Durations – Develop Schedule – Control Schedule Define Activities Sequence Activities Estimate Activity Resources Estimate Activity Durations Develop Schedule Control Schedule
- 42. Define Activities Enterprise Environmental Factors Organizational Process Assets ProjectScope Statement Decomposition Templates Rolling wave planning Expert judgment Planning component Inputs OutputsTools & Techniques Work Breakdown Structure WBS Dictionary Project Management Plan Activity List Activity Attributes Milestone List Requested Changes Define Activities Sequence Activities Estimate Activity Resources Estimate Activity Durations Develop Schedule Control Schedule
- 43. Define Activities • RollingWave Planning – Progressive planning where near term work is broken down in detail and distant work is kept at a higher WBS level • Planning Component – WBS items that cannot be broken down into work packages are put in a: – Control Account – High level planning dates for the scope to be defined – Planning Package – Package includes scope to be completed but no activities.
- 44. Sequence Activities Project Scope Statement ActivityList Activity Attributes Precedence diagramming method (PDM) Arrow diagramming method (ADM) Schedule network templates Dependency determination Applying leads and lags Inputs OutputsTools & Techniques Milestone List Approved Change Requests Project Schedule Network Diagrams Activity List Updates Activity Attributes Updates Requested Changes Define Activities Sequence Activities Estimate Activity Resources Estimate Activity Durations Develop Schedule Control Schedule
- 45. Precedence Diagramming Method(PDM) • Commonly called Activity on Node (AON), most commonly used sequencing method • Boxes are used to represent tasks with arrows used for dependencies
- 46. Estimate Activity Resources Enterprise Environmental Factors Organizational ProcessAssets Activity List Expert judgment Alternatives analysis Published estimating data Project management software Bottom-up estimating Inputs OutputsTools & Techniques Activity Attributes Resource Availability Activity Resource Requirements Activity Attributes Updates Resource Breakdown Structure Resource Calendar UpdatesProject Management Plan Requested Changes Define Activities Sequence Activities Estimate Activity Resources Estimate Activity Durations Develop Schedule Control Schedule
- 47. Estimate Activity Durations Enterprise EnvironmentalFactors Organizational Process Assets Project Scope Statement Expert judgment Analogous estimating Parametric estimating Three-point estimates Reserve Analysis Inputs Outputs Tools & Techniques Activity List Activity Resource Requirements Activity Duration Estimates Activity attributes updates Resource Calendar Activity Attributes Project Management Plan •Risk Register •Activity Cost Estimates Define Activities Sequence Activities Estimate Activity Resources Estimate Activity Durations Develop Schedule Control Schedule
- 48. Estimating Methods • CPM(Critical Path Method) – One time estimate per task – Controls cost with flexible schedule – Only on AOA networks (can have dummies) • PERT (Program Evaluation and Review Technique) – Three estimates per activity (Optimistic, Pessimistic, most likely) – Emphasis on meeting schedule with flexible cost – Only on AOA networks (can have dummies)
- 49. Estimating with PERT •PERT Formula (Expected Duration) – =(P+4M+O)/6 • Standard Deviation = (P-O)/6 • Variance = [(P-O)/6]2 Task O Optimistic M Most Likely P Pessimistic PERT (Expected Duration) Std Dev Variance A 2 days 4 days 8 days 4.3 days 1 day 1 day
- 50. Develop Schedule Enterprise Environmental Factors OrganizationalProcess Assets Project Scope Statement Schedule network analysis Critical path method Schedule compression What-if analysis Resource leveling Critical chain method Project management software Applying calendars Adjustable leads and lags Schedule model Inputs Outputs Tools & Techniques Activity List Activity Resource Requirements Schedule baseline Activity attributes updates Resource Calendar Activity Attributes Project Management Plan •Risk Register •Activity Cost Estimates Project schedule Schedule model data Resource requirements updates Requested changes Project management plan updates •Schedule management plan updates Project calendar updates Define Activities Sequence Activities Estimate Activity Resources Estimate Activity Durations Develop Schedule Control Schedule
- 51. Scheduling from Estimates •Critical Path – Longest time through the network diagram, the shortest time the project is expected to take • Slack (or Float) – The amount of time a task can be delayed without impacting the project – Calculated using: • Late Start – Early Start (LS-ES) Or • Late Finish – Early Finish (LF-EF) – Early Starts computed by making a “forward pass” through the network while late starts are computed using a “backward pass”
- 52. Critical Path Determination •EF=ES+DUR-1 • LS=LF-DUR+1 • Slack=LF-EF or LS-ES Task Name ES LS EF LF DUR Slack 4 2 2 23 1 9 863 2 10 8 9 0 10 4 3 0 7 8 1 0 2 Task A Task B Task C Task D
- 53. Control Schedule Schedule Management Plan ScheduleBaseline Schedule network analysis Critical path method Schedule compression What-if analysis Resource leveling Critical chain method Project management software Applying calendars Adjustable leads and lags Schedule model Inputs Outputs Tools & Techniques Performance reports Schedule baseline updates Requested changes Approved Change Requests Schedule model data updates Performance measurements Organizational process assets updates Activity list updates Recommended corrective actions Activity attribute updates Project Management Plan updates Define Activities Sequence Activities Estimate Activity Resources Estimate Activity Durations Develop Schedule Control Schedule
- 54. Other Important Terms •Lag – Inserted waiting time between tasks • Free Slack – Available delay time without impacting start of successor • Total Slack – Amount of time a task can be delayed without delaying project completion date • Project Slack – Amount of time a project can be delayed without impacting completion dates imposed by client • Crashing – Adding resources to critical path items to shorten schedule • Fast Tracking – Performing critical path tasks in parallel rather than series • Resource Leveling – Adjusting completion dates of tasks to meet available resources • Heuristics – Rules of thumb