Program Evaluation and Review Technique Article

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Category: Planning/ Monitoring - Control

Program (Project) Evaluation and Review Technique (PERT)(G) is a project management tool used to schedule, organize, and coordinate tasks within a project. It is basically a method to analyze the tasks involved in completing a given project, especially the time needed to complete each task, and to identify the minimum time needed to complete the total project. PERT planning involves the following steps:      

Identify the specific activities and milestones. Determine the proper sequence of the activities. Construct a network diagram. Estimate the time required for each activity. Determine the critical path. Update the PERT chart as the project progresses.

Program Evaluation and Review Technique (PERT), nodes, PERT event, predecessor event, successor event, PERT activity, Optimistic time, Pessimistic time, Most likely time, Expected time, Critical Path, Lead time, Lag time, Slack.

The main objective of PERT is to facilitate decision making and to reduce both the time and cost required to complete a project.

PERT is intended for very large-scale, one-time, non-routine, complex projects with a high degree of intertask dependency, projects which require a series of activities, some of which must be performed sequentially and others that can be performed in parallel with other activities.

Critical Path Method (CPM), Gantt chart


PERT planning involves the following steps that are described below. 1. Identify the specific activities and milestones. The activities are the tasks required to complete a project. The milestones are the events marking the beginning and the end of one or more activities. It is helpful to list the tasks in a table that in later steps can be expanded to include information on sequence and duration. 2. Determine the proper sequence of the activities. This step may be combined with the activity identification step since the activity sequence is evident for some tasks. Other tasks may require more analysis to determine the exact order in which they must be performed. 3. Construct a network diagram. Using the activity sequence information, a network diagram can be drawn showing the sequence of the serial and parallel activities. Each activity represents a node in the network, and the arrows represent the relation between activities. Software packages simplify this step by automatically converting tabular activity information into a network diagram. 4. Estimate the time required for each activity. Weeks are a commonly used unit of time for activity completion, but any consistent unit of time can be used. A distinguishing feature of PERT is its ability to deal with uncertainty in activity completion time. For each activity, the model usually includes three time estimates: 

Optimistic time – generally the shortest time in which the activity can be completed. It is common practice to specify optimistic time to be three standards deviations from the mean so that there is a approximately a 1% chance that the activity will be completed within the optimistic time. Most likely time – the completion time having the highest probability. Note that this time is different from the expected time. Pessimistic time – the longest time that an activity might require. Three standard deviations from the mean is commonly used for the pessimistic time.

PERT assumes a beta probability distribution for the time estimates. For a beta distribution, the expected time for each activity can be approximated using the following weighted average:   

Expected time = ( Optimistic + 4 x Most likely + Pessimistic ) / 6 This expected time may be displayed on the network diagram. To calculate the variance for each activity completion time, if three standard deviation times were selected for the optimistic and pessimistic...
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