Program Evaluation and Review Technique
PERT is a widely used method for planning and coordinating large-scale projects.
To obtain:
• A graphical display of project activities.
• An estimate of how long the project will take.
• An indication of which activities are the most critical to timely project completion.
• An indication of how long any activity can be delayed without delaying the project.
The Network Diagram
Network (precedence) diagram
-Diagram of project activities that shows sequential relationships by the use of arrows and nodes.
2 Different Conventions:
1. Activity-on-arrow ( AOA)
-Network diagram convention in which arrows designate activities.
2. Activity-on-node (AON)
-Network diagram convention in which nodes designate activities.
Activities
-Project steps that consume resources and/or time.
Events
-The starting and finishing of activities, designated by nodes in the AOA convention.
Deterministic time estimates
The main determinant of the way PERT and CPM networks are analyzed and interpreted is whether activity time estimates are PROBABILISATIC or DETERMINISTIC.
PROBABILISATIC
Estimates of time that allow for variation.
DETERMINISTIC
Time estimates that are fairly certain.
PROBABILISTIC TIME ESTIMATES
Three Time Estimates:
1. Optimistic Time ( to ) – the length of time required under optimum conditions
2. Pessimistic Time ( tp ) – the length of time required under the worst conditions
3. Most likely time ( tm* ) –the most probable amount of time required
Beta Distribution
• used to describe probabilistic time estimates.
In special interest in network analysis is the average or expected time for each activity and the variance of each activity time. The expected time of analysis is a weighted average of the three estimates: te- expexted time ∂2 - variance of each activity time
ta + 4tm +tp te= ----------------------- 6
The expected duration of a path is equal to the sum of the expected times of the
To obtain:
• A graphical display of project activities.
• An estimate of how long the project will take.
• An indication of which activities are the most critical to timely project completion.
• An indication of how long any activity can be delayed without delaying the project.
The Network Diagram
Network (precedence) diagram
-Diagram of project activities that shows sequential relationships by the use of arrows and nodes.
2 Different Conventions:
1. Activity-on-arrow ( AOA)
-Network diagram convention in which arrows designate activities.
2. Activity-on-node (AON)
-Network diagram convention in which nodes designate activities.
Activities
-Project steps that consume resources and/or time.
Events
-The starting and finishing of activities, designated by nodes in the AOA convention.
Deterministic time estimates
The main determinant of the way PERT and CPM networks are analyzed and interpreted is whether activity time estimates are PROBABILISATIC or DETERMINISTIC.
PROBABILISATIC
Estimates of time that allow for variation.
DETERMINISTIC
Time estimates that are fairly certain.
PROBABILISTIC TIME ESTIMATES
Three Time Estimates:
1. Optimistic Time ( to ) – the length of time required under optimum conditions
2. Pessimistic Time ( tp ) – the length of time required under the worst conditions
3. Most likely time ( tm* ) –the most probable amount of time required
Beta Distribution
• used to describe probabilistic time estimates.
In special interest in network analysis is the average or expected time for each activity and the variance of each activity time. The expected time of analysis is a weighted average of the three estimates: te- expexted time ∂2 - variance of each activity time
ta + 4tm +tp te= ----------------------- 6
The expected duration of a path is equal to the sum of the expected times of the