Program Evaluation and Review Technique (PERT) and Critical Path Method both are project schedule development and analysis techniques. Both these techniques establish the critical path in a schedule network diagram. However, both CPM and PERT use different approach to arrive at the critical path and activity duration estimates. The following blog post highlights difference Between CPM and PERT. Show
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Program Evaluation and Review Technique (PERT)The following paragraphs provide a brief overview of the Program Evaluation and Review Technique (PERT). What is PERT?Program Evaluation And Review Technique (PERT) is a schedule development and analysis technique. It represents the logical sequence of project schedule activities with their relationship in a graphical format. In 1957, United States Navy, Booz Allen Hamilton and Lockheed Cooperation developed Program Evaluation And Review Technique (PERT) to cater for Polaris missile / submarine projects. PERT Network DiagramHowever, PERT uses Arrow Diagram Method (ADM) technique to represent the logical sequence of project schedule activities. Activity-on-Arrow (AOA) diagramming method is an example of ADM technique to construct the project schedule network logic. PERT EstimatesMoreover, PERT uses probabilistic time estimates to determine the probability of project completion date. Further, it also facilitates calculation of risk involved in project completion date based on beta distribution of each activity time and normal distribution of the expected time. PERT Application & UsagePERT finds its usage when there is a high degree of uncertainty. Moreover, it uses weighted average formula of three-point estimation technique to calculate the expected activity duration. This helps to calculate activity duration when there is a high degree of uncertainty. Since PERT accounts for uncertainty and risk the expected duration is more accurate than the single point estimation technique. PERT further allows representation of large amounts of data for further analysis and modelling. Effect of changes on schedule as a result of changes in resources can be evaluated fairly easily. Program Evaluation and Review Technique mainly helps to control time element of projects. PERT is also used for those projects where percent complete is impossible to determine except for completed milestone. Research and Development projects especially the development side of the project uses PERT.
Critical Path Method (CPM)The following paragraphs provides basic details of Critical Path Method (CPM) schedule analysis technique. What is CPM?Critical Path Method (CPM) is also a schedule development and analysis technique. Morgan R. Walker of DuPont and James E. Kelley Jr. of Remington Rand developed Critical Path Method (CPM) in 1958. Diagramming Techniques in CPMThe critical path method analysis uses Precedence Diagram Method (PDM) technique to construct the schedule network logic. Precedence Diagramming Method is a technique that uses logical relationship among schedule activities to construct the network diagram. Activity-On-Node (AON) is one such technique that uses PDM method to construct the schedule network logic.
CPM ApplicationMoreover, Critical Path Method (CPM) finds application in construction projects. Further, Critical Path Method uses deterministic (single point) activity time estimates. However, CPM can control both time and cost aspect of the project. Moreover, the modern-day scheduling software also provide PERT analysis of the schedule developed. Unlike PERT, critical path method controls both time and cost aspect of a project. Today, Critical Path Method (CPM) is the most popular schedule network analysis technique. Moreover, most of the planning and scheduling programs use CPM technique to analyse the schedule. Hence, out of the two, Critical Path Method is the most widely used project schedule network analysis technique.
CPM and PERT Comparison ChartAttributesCritical Path Method (CPM)Program Evaluation and Review Technique (PERT)Year Introduced19581957Authors / OrganizationMorgan R. Walker of DuPont and James E. Kelley Jr. of Remington RandUnited States Navy, Booz Allen Hamilton and Lockheed CooperationApplicationActivity duration are fairly known.Highly uncertain activity duration.Project TypesConstructionResearch & DevelopmentEstimate TypesDeterministicProbabilisticCalculation MethodSingle point estimates3 point estimatesNetwork Diagram Method / TechniquePrecedence Diagramming Method (PDM)Arrow Diagramming Method (ADM)Network Diagram TypeActivity-on-Node (AON)Activity-on-Arrow (AOA)ControlsSchedule & CostScheduleComplexityLowHighPopularityHighLowSchedule Risk CalculationAdditional techniques are requiredYesProbability of Project CompletionAdditional techniques are requiredYesAccuracy of estimatesLowHighExplanationCritical Path Method Schedule AnalysisProgram Evaluation Review Technique PERTFormulasCritical Path Analysis FormulasPERT Formulas
CPM and PERT ConclusionProject Management Body of Knowledge (PMBOK)® recognizes only CPM and other techniques like Critical Chain Method (CCM) as a scheduling methodology. Moreover, PMBOK mentions PERT’s three point estimation technique as a tool for duration and cost estimates. As a matter of fact, from PMP certification exam point of view understanding critical path analysis is sufficient. However, PERT is an equally important scheduling technique necessary to broaden the project scheduling knowledge base. What is the difference between the Program Evaluation and Review Technique PERT and Critical Path Method CPM )?The main difference between PERT and CPM is that PERT focuses on time planning and time management, with a goal of delivering the project as quickly as possible. CPM focuses on time and budgeting, which is useful for bringing in the project on budget as well as on time.
Which is more accurate PERT or CPM?PERT technique is best suited for a high precision time estimate, whereas CPM is appropriate for a reasonable time estimate. PERT deals with unpredictable activities, but CPM deals with predictable activities. PERT is used where the nature of the job is non-repetitive.
What is the difference between a PERT chart and a critical path diagram?The main difference between PERT and Critical Path is knowing how long a given task will take. With PERT, task durations are variable, hence the need to predict time using a model. Critical Path is more useful for projects where task length is easy to predict, such as a construction project or a large conference.
What is the main difference between PERT and CPM quizlet?The basic difference between PERT and CPM is that PERT requires three time estimates of activity completion time, whereas CPM uses only a single estimate. The ES of an activity that has only one predecessor is simply the EF of that predecessor.
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