Project Scheduling techniques in Project PERT.pptx
- 3. CONTENTS INTRODUCTION NETWORK SCHEDULING PERT CALCULATIONS (EXAMPLES) CRITICAL PATH METHOD TECHNIQUES FOR NETWORK SCHEDULING ADVANTAGES/DISADVANTAGES OF PERT PROGRAM EVALUATION & REVIEW TECHNIQUE COMPARISON OF CPM & PERT ADVANTAGES/DISADVANTAGES OF CPM CPM CALCULATIONS (EXAMPLES)
- 4. INTRODUCTION
- 5. Scheduling is process of determining the interrelationship of associated timings of operations. Basis for monitoring and controlling project. Based on Work Breakdown Structure (WBS) PROJECT SCHEDULING
- 7. NETWORK SCHEDULING Network Scheduling is a method of scheduling activities by joining them in a series of inter- connected links which reflect relationships of activities as assigned by the planner
- 8. The project can be broken down into a group of activities. Each activity can be assigned a duration. The logic relationship between activities are known and fixed in the network chain. BASIC ASSUMPTIONS FOR A NETWORK SCHEDULE
- 9. Both use same calculations, almost similar. Main difference is probabilistic and deterministic in time estimation. PERT CPM Program Evaluation and Review Technique developed by the US Navy with Booz Hamilton Lockheed for the Polaris Missile/Submarine program 1958 Critical Path Method Developed by El Dupont for Chemical Plant Shutdown Project- about same time as PERT TECHNIQUES FOR NETWORK SCHEDULING
- 10. PROGRAM EVALUATION & REVIEW TECHNIQUE (PERT)
- 11. DEFINITION The program (or project) evaluation and review technique, commonly abbreviated PERT, is a statistical tool, used in project management, which was designed to analyse and represent the tasks involved in completing a given project & to illustrate the flow of events in a project.
- 12. In certain projects like research and development, new product introductions, it is difficult to estimate the time of various activities. Hence PERT is used in such projects with a probabilistic method using three time estimates for an activity, rather than a single estimate, as shown in Figure. Fig: PERT using probabilistic Method with 3 Time Estimation CONT..
- 13. OPTIMISTIC TIME (t0): “ If every thing goes well.” It is minimum time in the past data but not a crash time. PESSIMISTIC TIME (tP): “If every thing goes badly”. It is maximum time in past data. MOST LIKELY TIME (tm): “The average of all normal times in past data”. 3 PERT DURATIONS
- 14. The activity duration is subjected to variability due to i. Varying resource demand ii. Work process itself iii. Insufficient data available to estimate for characterizing the work process exactly. REASONS FOR VARIABILITY IN ACTIVITY DURATION
- 15. “Probability is a measure of uncertainty” Everyone knows the meanings of the statement that an event is Almost Certain Highly Probable About 50-50 Highly Unlikely Highly Improbable CONT..
- 16. PERT only attempts to quantify these statements in a precise and objective way. Probability is expressed on a scale that runs from 0 to 1 Zero(0) represent “IMPOSSIBALITY” One(1) represent “CERTAINTY” The number in between zero and one represent varying degree of likelihood. That is why probability is known to be a measure of uncertainty CONT..
- 17. PERT PLANNING INVOLVE THE FOLLOWING STEPS: 2)Determine the proper sequence of the activities 3)Construct a network diagram 4) Estimate the time require for each activity 5) Determine the critical path 1) Identify the specific activity & events PROCESS
- 18. 1) Identify Activities & Events : The activities are tasks require to complete the project. The events marking the beginning & end of one or more activities. 2)Determine the proper sequence of the activities : This step may be combine with the activity identification step since the activity sequence is event for some task . Other tasks may require more analysis to determine exact order in which they must be perform . CONT..
- 19. 3.Construct a network diagram : Using the activity sequence information , a network diagram can be drawn showing the sequence of the serial & parallel activities. The activities are depicted by arrow lines & milestones are depicted by circles. 4.Estimate the time required for activity : A distinguishing feature of PERT is its ability to deal with uncertainty in activity completion times by using the 3 time estimates. CONT..
- 20. 5. Determine the critical path : The critical path is determine by adding the times for the activities in each sequence & determining the longest path in project. The critical path determines the total time required. 6.Update the PERT chart as the project progresses : Make adjustment in the PERT chart as the project progresses. As the project unfolds ,the estimated times can be replaced with actual times. The PERT chart may be modified & improved to reflect the new situation. CONT..
- 22. Taking all three time estimates into consideration, the expected time of an activity is arrived at. The average or mean (ta) value of the activity duration is given by The variance of the activity time is calculated using the formula, PERT CALCULATION
- 23. variance is zero Activity duration is characterized only by tm = to= tP Activity duration becomes a deterministic not probabilistic quantity WHEN “TO & TP” COINCIDES
- 24. . DR. LIAQAT ALI QURESHI NORMAL DISTRIBUTION CURVE -3 -2 +3 +2 -1 +1 Frequency of occurrence Scale of random variable “t” te 96% of the area 99.7% of the area 68% of the area
- 25. For construction engineering accuracy, probabilities beyond “ 1% “ are generally not required The area under the density curve between +1 standard deviation and -1 standard deviation is approximately 68% . Between “+2 and -2 “ is 96% Between +3 and -3 standard deviation is 99.7% DR. LIAQAT ALI QURESHI CONT…
- 26. PROJECT’S EXPECTED COMPLETION TIMES By implying central limit theorem Probability of completing a project by any specific time, TS , can be determined by using Z-table based on the standard or normal distribution density curve Ta = Critical Path’s mean Longest path standard Deviation= TS = Any date you choose Z = Number of deviation from mean 𝑍= 𝑇𝑆−𝑇𝑎 𝜎𝑇 𝜎𝑇𝑎=¿ (𝜎𝑇 𝑎)1/2 DR. LIAQAT ALI QURESHI
- 27. Z-TABLE (STANDARD NORMAL DISTRIBUTION TABLE) Z P* Z P* 3 0.999 -3 0.001 2.5 0.994 -2.5 0.006 2 0.997 -2 0.023 1.9 0.971 -1.9 0.029 1.8 0.964 -1.8 0.036 1.7 0.955 -1.7 0.045 1.6 0.945 -1.6 0.055 1.5 0.933 -1.5 0.067 1.4 0.919 -1.4 0.081 1.3 0.903 -1.3 0.097 1.2 0.885 -1.2 0.115 1.1 0.864 -1.1 0.136 1.0 0.841 -1.0 0.159 0.9 0.816 -0.9 0.184 0.8 0.788 -0.8 0.212 0.7 0.758 -0.7 0.242 0.6 0.726 -0.6 0.274 0.5 0.692 -0.5 0.308 0.4 0.655 -0.4 0.345 0.3 0.618 -0.3 0.382 0.2 0.579 -0.2 0.421 0.1 0.540 -0.1 0.460 0.0 0.500 0.0 0.500 P* = Probability of completing by TA
- 28. 3 Pert durations of the activities of a project are given below. If critical path consists of A-B- D-F-G, find the following: 1)Ta2) σT 3) Probability that the project will close: (a) By the end of day 31 (b) Before the start of day 37 (c) During day 34 (d) On days 34, 35, & 36 4) Find the date of completion with at least 93 percent confidence. EXAMPLE 1
- 29. Activity tO tm tP A 4 6 8 B 1 7 13 C 5 6 7 D 5 5 11 E 2 4 8 F 1 5 7 G 7 7 7 CONT...
- 30. SOLUTION Critical Act. t0 tm tP ta σ2 t A 4 6 8 6.0 0.45 B 1 7 13 7.0 4.00 D 5 5 11 6.0 1.00 F 1 5 7 4.7 1.00 G 7 7 7 7.0 0.00 TOTAL ∑30.7 ∑6.45
- 31. Ta = ∑ta rounded to whole number = 31 σT = √ ∑ σ2 = √ 6.45 = 2.54 TA & σT
- 32. By the end of day “X” = z-x = P-X During day “X” = ZX = PX During days “X,Y,Z” = ZXYZ = PXYZ After the end of day “X” = ZX- = PX- NOTATION TO BE USED
- 33. Z-31 = (Ts - TE) /σT = 31 - 31 / 2.54 = 0 P-31 = 0.50 = 50 % (A) BY THE END OF DAY 31
- 34. (It is equivalent to “By the end of day 36) Z-36 = (Ts - TE) /σTE = 36 - 31 / 2.54 = 1.97 P-36 = 0.98 = 98 % (B) BEFORE THE START OF DAY 37
- 35. It is equivalent to “By the end of day 34 - By the end of day 33” Z-34 = (Ts - TE) /σTE = 34 - 31 / 2.54 = 1.18 P-34 = 0.88 = 88 % Z-33 = (Ts - TE) /σTE = 33 - 31 / 2.54 = 0.79 P-33 = 0.79 = 79 % P34 = P-34 - P-33 = 88 - 79 = 9% (C) DURING DAY 34
- 36. It is equivalent to “By the end of day 36 - By the end of day 33” P34,35,36 = P-36 - P-33 = 98 (from b) - 79 (from c) = 19% (D) ON DAYS 34, 35, & 36
- 37. P = 93 % Z = 1.5 (from table) Z = (Ts - TE) /σTE 1.5 = (Ts - 31) / 2.54 Ts = 34.81 Therefore, the completion date = end of day 35 with at least 93 % confidence. DATE OF COMPLETION (WITH 93 % CONFIDENCE)
- 38. An R & D project has a list of tasks to be performed whose time estimates are given in the Table as follows : EXAMPLE 2 a.Draw the project network. b.Find the critical path. c.Find the probability that the project is completed in 19 days. If the probability is less that 20%, find the probability of completing it in 24 days.
- 39. Time expected for each activity is calculated using the formula Similarly, the expected time is calculated for all the activities. CONT.. The variance of activitytime is calculated using the formula Similarly,variances of all the activities are calculated.
- 40. ESTIMATED TIME & VARIANCE CALCULATED
- 41. Calculate the earliest time, ES and Latest time LS for all the activities. B) From the network diagram the critical path is identified as 1-4, 4-6, 6-7, with a project duration of 22 days. A) CONSTRUCT A NETWORK DIAGRAM 9 9 ES LS
- 42. from normal tables, z (-1.3416) = 0.0901 = 0.0901 = 9.01% (C)The probability of completing the project within 19 days is given by P (Z< Z0 ) To find Zo, Thus, the probability of completing the R & D project in 19 days is 9.01%.
- 43. Since the probability of completing the project in 19 days is less than 20% As in question, we find the probability of completing it in 24 days. CONT… from normal tables, z (0.8994) = 0.802 = 0.802 = 80.2%
- 45. Simple to understand and use. Show whether the project is on schedule; or behind /ahead of the schedule. Identify the activities that need closer attention Determine the flexibility available with activities Show potential risk with activities Provide good documentation of the project activities Help to set priorities among activities & resource allocation as per priority ADVANTAGES
- 46. Time Focused Method Subjective Analysis Prediction Inaccuracy Expensive – Too expensive in terms of time consumed, research, prediction, and resources utilized. Other Issues with PERT – This method is highly labor-intensive in nature. DISADVANTAGES
- 48. ADVANTAGES OF CPM Consistent framework for planning, scheduling, monitoring, and controlling project. Helps proper communications between departments and functions. Determines expected project completion date. Determines the dates on which tasks may be started or must be started if the project is to stay in schedule. Shows which tasks must be coordinated to avoid resource or timing conflicts. Shows which tasks may run in parallel to meet project completion date. 48
- 49. DISADVANTAGES OF CPM Reliability of CPM largely based on accurate estimates and assumptions made. CPM does not guarantee the success of project. Resources may not actually be as flexible as management hope when they come to address network float. Too many activities may the network diagram too complicated. Activities might themselves have to be broken down into mini projects. 49
- 51. COMPARISON CHART Basis for Comparison PERT CPM Meaning PERT is a project management technique, used to manage uncertain activities of a project. CPM is a statistical technique of project management that manages well defined activities of a project. What is it? A technique of planning and control of time. A method to control cost and time. Orientation Event-oriented Activity-oriented Evolution Evolved as Research & Development project Evolved as Construction project Model Probabilistic Model Deterministic Model
- 52. Basis for Comparison PERT CPM Focuses on Time Time-cost trade-off Estimates Three time estimates One time estimate Appropriate for High precision time estimate Reasonable time estimate Management of Unpredictable Activities Predictable activities Nature of jobs Non-repetitive nature Repetitive nature Suitable for Research and Development Project Non-research projects like civil construction, ship building etc.
- 53. REFERENCES Frame,J.Davidson.Managingprojectsinorganizations:howtomakethebestuseoftime,techniques, andpeople.SanFrancisco:JosseyBass,1995 Heldman,Kim.Projectmanagementjumpstart.SanFrancisco:SybexBooks,2003. Miller,"Schedule,CostandProfitControlwithPERT,"McGraw-Hill, 1963 Moder&Phillips,"ProjectManagementwithCPM,PERTandPrecedenceProgramming,"2dE 1983 https://www.assignmentpoint.com/business/accounting/advantages-disadvantages- pert-cpm.html Frame, J. Davidson. The new project management : tools for an age of rapid change, complexity, and otherbusinessrealities.SanFrancisco:JohnWiley&Sons,Inc., 2002 Heerkens,GaryR.Projectmanagement.NewYork:McGraw-Hill, 2002 https://www.geeksforgeeks.org/pert-planning-process/?ref=rp
- 54. QUESTIONS
Editor's Notes
- #9: The only difference between the two method is that CPM uses fixed duration for each activity while Pert uses a probability distribution
- #13: Optimistic time tO: It is the shortest time taken to complete the activity. It means that if everything goes well then there is more chance of completing the activity within this time. Most likely time tm: It is the normal time taken to complete an activity, if the activity were frequently repeated under the same conditions. Pessimistic time tp: It is the longest time that an activity would take to complete. It is the worst time estimate that an activity would take if unexpected problems are faced.