Pert

P ROGRAM EVALUATION A ND REVIEW TECHNIQUE ( PERT)
Category: Planning/ Monitoring - Control

A BSTRACT
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 eachtask, 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 theproject progresses.

K EYWORDS
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.

O BJECTIVE
The main objective of PERT is to facilitate decision making and to reduce both
the time and cost required to complete aproject.

F IELD OF APPLICATION
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.

R ELATED TOOLS
Critical Path Method (CPM), Gantt chart

1

D ESCRIPTIONPERT planning involves the following steps that are described below.
1. Identify the specific activities and mil estones. 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 infor mation on
sequence andduration.
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 showingthe sequence of the serial and
parallel activities. Each activity represents a node in the netw ork, 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, butany 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 themean 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 thepessimistic
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...