Program evaluation and review technique (PERT)
Prepared By
Luay Kadhum Hameed
2009
CHAPTER 1
Introduction
A project defines a combination of interrelated activities that
must be executed in a certain order before the entire task can be
completed. The activities are interrelated in a logic sequences in the sense
that some activities cannot start until others are completed .An activity in
a project is usually viewed as a job requiring time and resources for its
completion .In general ,a project is a one –time effort ;that is, the same
sequence of activities may not be repeated in the future.
In the past ,the scheduling of a project (over time) was done with little
specifies the start and finish for each activity on a horizontal time scale .
Its disadvantage is that the interdependency between the different
activities(which mainly controls the progress of the project)cannot be
determined from the bar chart .The growing complexities of today's
project have demanded more systematic and more effective planning
techniques with the objective of optimizing the efficiency of executing
the project .Efficiency here implies effecting almost reduction in the time
required to complete the project while accounting for the economic
feasibility of using available resources .
Project management has evolved as a new field with the development of
two analytic technique for planning, scheduling, and controlling of
projects.
These are the critical path method (CPM) and the project evaluation and
review technique (PERT) . the two techniques were developed by two
different groups almost simultaneously (1956- 1958)CPM was first
developed by E.Idu Pout de Nemours and company as an application to
construction projects and was later extended to a more advanced status by
Mauchly associates . PERT , on the other hand was developed for the
U.S. Navy by a consulting firm for scheduling the research and
development activities for the Polaris missile program.
PERT and CPM are basically time –oriented methods in the sense that
they both lead to the determination of a time schedule . Although the two
methods were developed independently , they are strikingly similar .
Perhaps the most important difference is that originally the time estimates
for the activities were assumed deterministic in CPM and probabilistic in
PERT. Today , PERT and CPM actually comprise one technique and the
differences , if any,are only historical . Consequently , both techniques
will be referred to as "project scheduling" techniques.
Project scheduling by PERT-CPM consist of three basic phase, planning,
Scheduling, and controlling.
The planning phase is initiated by breaking down the project into distinct
activities . The time estimates for these activities are then determined and
a network (or arrow)diagram is constructed with each of its arcs(arrows)
representing an activity. The entire arrow diagram gives a graphic
representation of the interdependencies between the activities of the
project. The construction of the arrow diagram as a planning phase has
the advantage of studying the different jobs in detail .perhaps suggesting
improvement before the project is actually executed . More important will
be its use to develop a schedule for the project.
The ultimate objective of the Scheduling phase is to construct a time chart
showing the start and finish times for each activity as well as its
relationship to other activities in the project. In addition, the Schedule
must pinpoint the critical (in view of time) activities that require special
attention if the project is to be completed on time. For the non critical
activities the schedule must show the amount of slack or float time that
can be used advantageously when such activities are delayed or when
limited resources are to be used effectively .
The final phase in project management is project control .This include the
use of the arrow diagram and the time chart for making periodic progress
reports. The network may thus be updated and analyzed and, if necessary,
a new schedule is determined for the remaining portion of the project.
CHAPTER 2
Project management
Project management is concerned with the overall planning and
co-ordination of a project from conception to completion aimed at
meeting the stated requirements and ensuring completion on time, within
cost and to required quality standards. Project management is normally
reserved for focused, non-repetitive, time-limited activities with some
degree of risk and that are beyond the usual scope of operational activities
for which the organization is responsible.
A project is a temporary endeavour involving a connected sequence of
activities and a range of resources, which is designed to achieve a specific
and unique outcome and which operates within time, cost and quality
constraints and which is often used to introduce change.
Characteristic of a project







A unique, one-time operational activity or effort
Requires the completion of a large number of interrelated activities
Established to achieve specific objective
Resources, such as time and/or money, are limited
Typically has its own management structure
Need leadership
project management
 The application of a collection of tools and techniques to direct the
use of diverse resources towards the accomplishment of a unique,
complex, one time task within time, cost and quality constraints.
 Its origins lie in World War II, when the military authorities used
the techniques of operational research to plan the optimum use of
resources.
 One of these techniques was the use of networks to represent a
system of related activities
Project Management Process
 Project planning
 Project scheduling
 Project control
 Project team
-made up of individuals from various areas and departments within a
company
 Matrix organization
-a team structure with members from functional areas, depending on
skills required
 Project Manager
-most important member of project team
 Scope statement
-a document that provides an understanding, justification, and
expected result of a project
 Statement of work
-written description of objectives of a project
 Organizational Breakdown Structure
-a chart that shows which organizational units are responsible for
work items
 Responsibility Assignment Matrix
-shows who is responsible for work in a project
Work breakdown structure
 A method of breaking down a project into individual
elements ( components, subcomponents, activities and
tasks) in a hierarchical structure which can be scheduled
and cost
 It defines tasks that can be completed independently of
other tasks, facilitating resource allocation, assignment of
responsibilities and measurement and control of the project
 It is foundation of project planning
 It is developed before identification of dependencies and
estimation of activity durations
 It can be used to identity the tasks in the CPM and PERT
Project Planning
• Resource Availability and/or Limits
– Due date, late penalties, early completion incentives
– Budget
• Activity Information
– Identify all required activities
– Estimate the resources required (time) to complete each
activity
– Immediate predecessor(s) to each activity needed to create
interrelationships
Project Scheduling and Control Techniques
1.Critical Path Method (CPM)
2. Program Evaluation and Review Technique (PERT)
Project Network
•
Network analysis is the general name given to certain specific
techniques which can be used for the planning, management and
control of projects
• Use of nodes and arrows
Arrows
An arrow leads from tail to head directionally
– Indicate ACTIVITY, a time consuming effort that is
required to perform a part of the work.
Nodes
 A node is represented by a circle
- Indicate EVENT, a point in time where one or more
activities start and/or finish
• Activity
– A task or a certain amount of work required in the project
– Requires time to complete
– Represented by an arrow
• Dummy Activity
– Indicates only precedence relationships
– Does not require any time of effort
• Event
– Signals the beginning or ending of an activity
– Designates a point in time
– Represented by a circle (node)
• Network
– Shows the sequential relationships among activities using
nodes and arrows
 Activity-on-node (AON)
nodes represent activities, and arrows show precedence
relationships
 Activity-on-arrow (AOA)
arrows represent activities and nodes are events for points in time
Lay
foundation
1
3
Design house
and obtain
financing
2
3
2
Dummy
1
Order and
receive
materials
Finish
work
Build
house
0
4
6
3
Select 1
paint
1
5
1
Select
carpet
7
Fig (2-1) AOA Project Network for House
Lay foundations
Build house
4
3
2
2
Finish work
7
1
1
3
Start
Design house
and obtain
financing
3
1
Order and receive
materials
6
1
5
1
Select carpet
Select paint
Fig (2-2) AON Project Network for House
Situations in network diagram
A
B
C
Fig (2-3)
A must finish before either B or C can start
A
C
B
Fig (2-4) both A and B must finish before C can start
A
C
B
D
Fig (2-5) both A and C must finish before either of B or D can start
A
B
Dummy
C
D
Fig (2-6) A must finish before B can start
both A and C must finish before D can start
La y
foundation
2
La y
foundatio
n
3
3
2
0
Dumm
y
1
2
Order
material
Incorrect
precedence
relationship
4
Order
material
( a)
Correct
precedence
relationship
(b)
Fig (2-7) Concurrent Activities
CHAPTER 3
CPM - Critical Path Method
History of CPM
 E I Du Pont de Nemours & Co. (1957) for construction of new
chemical plant and maintenance shut-down
 Deterministic task times
 Activity-on-node network construction
 Repetitive nature of jobs
Planning a project usually involves dividing it into a number of small
tasks that can be assigned to individuals or teams. The project’s schedule
depends on the duration of these tasks and the sequence in which they are
arranged. This sequence can be driven by several factors: customer
deadlines, availability of personnel or resources, and dependencies among
tasks.
DuPont developed a Critical Path Method (CPM) designed to address the
challenge of shutting down chemical plants for maintenance and then
restarting the plants once the maintenance had been completed.
Complex project require a series of activities, some of which must be
performed sequentially and others that can be performed in parallel with
0ther activities.
This collection of series and parallel tasks can be modeled as a network.
CPM models the activities and events of a project as a network. Activities
are shown as nodes on the network and events that signify the beginning
or ending of activities are shown as arcs or lines between the nodes.
The Figure below shows an example of a CPM network diagram:
Fig (3-1) CPM network diagram
Steps in CPM Project Planning
1. Specify the individual activities.
2. Determine the sequence of those activities.
3. Draw a network diagram.
4. Estimate the completion time for each activity.
5. Identify the critical path (longest path through the network)
6. Update the CPM diagram as the project progresses.
1. Specify the individual activities
All the activities in the project are listed. This list can be used as the basis
for adding sequence and duration information in later steps.
2. Determine the sequence of the activities
Some activities are dependent on the completion of other activities. A list
of the immediate predecessors of each activity is useful for constructing
the CPM network diagram.
3. Draw the Network Diagram
Once the activities and their sequences have been defined, the CPM
diagram can be drawn. CPM originally was developed as an activity on
node network.
4. Estimate activity completion time
The time required to complete each activity can be estimated using past
experience. CPM does not take into account variation in the completion
time.
5. Identify the Critical Path
The critical path is the longest-duration path through the network. The
significance of the critical path is that the activities that lie on it cannot be
delayed without delaying the project. Because of its impact on the entire
project, critical path analysis is an important aspect of project planning.
The critical path can be identified by determining the following four
parameters for each activity:
• ES - earliest start time: the earliest time at which the activity can start
given that its precedent activities must be completed first.
• EF - earliest finish time, equal to the earliest start time for the activity
plus the time required to complete the activity.
• LF - latest finish time: the latest time at which the activity can be
completed without delaying the project.
• LS - latest start time, equal to the latest finish time minus the time
required to complete the activity.
The slack time for an activity is the time between its earliest and latest
start time, or between its earliest and latest finish time. Slack is the
amount of time that an activity can be delayed past its earliest start or
earliest finish without delaying the project.
The critical path is the path through the project network in which none of
the activities have slack, that is, the path for which ES=LS and EF=LF for
all activities in the path. A delay in the critical path delays the project.
Similarly, to accelerate the project it is necessary to reduce the total time
required for the activities in the critical path.
6. Update CPM diagram
As the project progresses, the actual task completion times will be known
and the network diagram can be updated to include this information.
A new critical path may emerge, and structural changes may be made in
the network if project requirements change.
CPM calculation
• Path
– A connected sequence of activities leading from the starting
event to the ending event
• Critical Path
– The longest path (time); determines the project duration
• Critical Activities
– All of the activities that make up the critical path
Forward Pass
The forward pass goes from the initial task (the task with no
predecessors) to the final task (the one with no successors), visiting every
task in every path and setting the ES and EF dates on the tasks.
The algorithm is similar to graph theory’s depth-first search, except that
the forward pass follows every path from initial to final task, while depthfirst search stops when it arrives at a task that it’s already visited. When
the forward pass arrives at a task, it may change that task’s ES and EF
dates, and that change must be carried forward to the final task. During
the forward pass, a task may be visited several times as different paths
through the network are followed. A task’s ES is determined by the
predecessor task with the latest EF, since a task can’t start until all of its
predecessors have finished.
• Earliest Start Time (ES)
– earliest time an activity can start
– ES = maximum EF of immediate predecessors
• Earliest finish time (EF)
– earliest time an activity can finish
– earliest start time plus activity time EF= ES + t
Backward Pass
he backward pass goes from the final task to the initial task, visiting
every task in every path and setting the LS and LF dates on the tasks.
It’s similar to the forward pass in that it arrives at a task, it may
change that task’s LS and LF dates, and that change must be carried
back to the initial task. The difference is:
• The forward pass sets the task’s latest ES, as determined by the EFs
of its predecessors
• The backward pass sets the task’s earliest LF, as determined by the
LSs of its successors.
The reason for the backward pass’s rule for setting LF is not as
obvious as the forward pass’s rule. Any start date, ES or LS, must be
after the corresponding finish dates of all of the task’s predecessors.
To maintain this consistency, the backward pass must set a task’s LF
to a value that’s earlier than the LS of any of the task’s successors.
 Latest Start Time (LS)
Latest time an activity can start without delaying critical path time
LS= LF - t
 Latest finish time (LF)
latest time an activity can be completed without delaying critical path
time
LS = minimum LS of immediate predecessors
CPM analysis
• Draw the CPM network
• Analyze the paths through the network
• Determine the float for each activity
– Compute the activity’s float
float = LS - ES = LF - EF
– Float is the maximum amount of time that this activity can
be delay in its completion before it becomes a critical
activity, i.e., delays completion of the project
• Find the critical path is that the sequence of activities and events
where there is no “slack” i.e.. Zero slack
– Longest path through a network
• Find the project duration is minimum project completion time
CHAPTER 4
Program Evaluation and Review Technique (PERT)




U S Navy (1958) for the POLARIS missile program
Multiple task time estimates (probabilistic nature)
Activity-on-arrow network construction
Non-repetitive jobs
The Program Evaluation and Review Technique (PERT) is a
network model that allows for randomness in activity completion times.
PERT was developed in the late 1950's for the U.S. Navy's Polaris project
having thousands of contractors. It has the potential to reduce both the
time and cost required to complete a project.
The Network Diagram
In a project, an activity is a task that must be performed and an event is a
milestone marking the completion of one or more activities. Before an
activity can begin, all of its predecessor activities must be completed.
Project network models represent activities and milestones by arcs and
nodes.
PERT is typically represented as an activity on arc network, in which the
activities are represented on the lines and milestones on the nodes. The
Figure 2-1 shows a simple example of a PERT diagram.
Figure(4-1) PERT diagram.
The milestones generally are numbered so that the ending node of an
activity has a higher number than the beginning node. Incrementing the
numbers by 10 allows for new ones to be inserted without modifying the
numbering of the entire diagram. The activities in the above diagram are
labeled with letters along with the expected time required to complete the
activity.
Steps in the PERT Planning Process
PERT planning involves the following steps:
1. Identify the specific activities and milestones.
2. Determine the proper sequence of the activities.
3. Construct a network diagram.
4. Estimate the time required for each activity.
5. Determine the critical path.
6. Update the PERT chart as the project progresses.
1. Identify activities and milestones
The activities are the tasks required to complete the project. The
milestones are the events marking the beginning and end of one or more
activities.
2. Determine activity sequence
This step may be combined with the activity identification step since the
activity sequence is known for some tasks. Other tasks may require more
analysis to determine the exact order in which they must be performed.
3. Construct the Network Diagram
Using the activity sequence information, a network diagram can be drawn
showing the sequence of the serial and parallel activities.
4. Estimate activity times
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 times. For each activity, the model usually includes
three time estimates:
• Optimistic time (OT) - generally the shortest time in which the activity
can be completed. (This is what an inexperienced manager believes!)
• Most likely time (MT) - the completion time having the highest
probability. This is different from expected time. Seasoned managers
have an amazing way of estimating very close to actual data from prior
estimation errors.
• Pessimistic time (PT) - the longest time that an activity might require.
The expected time for each activity can be approximated using the
following weighted average:
Expected time = (OT + 4 x MT+ PT) / 6
This expected time might be displayed on the network diagram.
Variance for each activity is given by: [(PT - OT) / 6]2
5. Determine the Critical Path
The critical path is determined by adding the times for the activities in
each sequence and determining the longest path in the project. The
critical path determines the total time required for the project.
If activities outside the critical path speed up or slow down (within
limits), the total project time does not change. The amount of time that a
non-critical path activity can be delayed without delaying the project is
referred to as slack time.
If the critical path is not immediately obvious, it may be helpful to
determine the following four quantities for each activity:
• ES - Earliest Start time
• EF - Earliest Finish time
• LS - Latest Start time
• LF - Latest Finish time
These times are calculated using the expected time for the relevant
activities. The ES and EF of each activity are determined by working
forward through the network and determining the earliest time at which
an activity can start and finish considering its predecessor activities.
The latest start and finish times are the latest times that an activity can
start and finish without delaying the project. LS and LF are found by
working backward through the network. The difference in the latest and
earliest finish of each activity is that activity's slack.
The critical path then is the path through the network in which none of
the activities have slack.
The variance in the project completion time can be calculated by
summing the variances in the completion times of the activities in the
critical path. Given this variance, one can calculate the probability that
the project will be completed by a certain date.
Since the critical path determines the completion date of the project, the
project can be accelerated by adding the resources required to decrease
the time for the activities in the critical path. Such a shortening of the
project sometimes is referred to as project crashing.
6. Update as project progresses
Make adjustments in the PERT chart as the project progresses. As the
project unfolds, the estimated times can be replaced with actual times. In
cases where there are delays, additional resources may be needed to stay
on schedule and the PERT chart may be modified to reflect the new
situation.
PERT analysis
 PERT is based on the assumption that an activity’s duration
follows a probability distribution instead of being a single value
 Three time estimates are required to compute the parameters of an
activity’s duration distribution:
te = Mean (expected time):
Variance: Vt =2 =
tp + 4 tm + to
6
tp - to
2
6
 Draw the network.
 Analyze the paths through the network and find the critical path.
 The length of the critical path is the mean of the project duration
probability distribution which is assumed to be normal
 The standard deviation of the project duration probability
distribution is computed by adding the variances of the critical
activities (all of the activities that make up the critical path) and
taking the square root of that sum
 Probability computations can now be made using the normal
distribution table.
Probability computation
Determine probability that project is completed within specified time
x-
Z=
Where

 = tp = project mean time
 = project standard mean time
x = (proposed ) specified time
Probabilit
y
Z

 = tp
x
Time
Figure(4-2) Normal Distribution of Project Time
PROJECT COST
Cost consideration in project
 Project managers may have the option or requirement to crash the
project, or accelerate the completion of the project.
 This is accomplished by reducing the length of the critical path(s).
 The length of the critical path is reduced by reducing the duration
of the activities on the critical path.
 If each activity requires the expenditure of an amount of money to
reduce its duration by one unit of time, then the project manager
selects the least cost critical activity, reduces it by one time unit,
and traces that change through the remainder of the network.
 As a result of a reduction in an activity’s time, a new critical path
may be created.
 When there is more than one critical path, each of the critical paths
must be reduced.
 If the length of the project needs to be reduced further, the process
is repeated.
Project Crashing
•
Crashing
– reducing project time by expending additional resources
• Crash time
– an amount of time an activity is reduced
• Crash cost
– cost of reducing activity time
• Goal
– reduce project duration at minimum cost
Activity cost
Activity crashing
Crash
cost
Crashing
activity
Slope = crash cost per unit time
Normal Activity
Normal
cost
Normal
time
Crash
time
Activity time
Figure(4-3) Time-Cost Relationship
 Crashing costs increase as project duration decreases
 Indirect costs increase as project duration increases
 Reduce project length as long as crashing costs are less than
indirect costs
cost
Min total cost
= optimal
project time
Total project cost
Indirect cost
Direct cost
time
Figure(4-3) Time-Cost Tradeoff
Case study
CPM
PERT
PERT/COST
PERT/CPM Chart
A project has been defined to contain the following list of activities along
with their required times for completion
Activity
No
1.
2.
3.
4.
5.
6.
7.
8.
Activity
Requirements
collection
Screen design
Report design
Database design
User documentation
Programming
Testing
Installation
Expected
completion time
5
Dependency
6
7
2
6
5
3
1
1
1
2,3
4
4
6
5,7
-
TE = 11
TE = 20
2
5
6
8
1
6
TE = 14
1
TE = 23
4
5
TE = 12
2
TE = 19
3
TE = 22
6
7
5
3
Fig(5-1) CPM Chart
Using information from the table, indicate expected completion time for
each activity.
2
6
5
TE = 14
8
1
6
TE = 5
1
5
4
TE = 12
2
3
TE = 19
TE = 22
6
7
5
3
Fig(5-2) CPM Chart with TE
Calculate earliest expected completion time for each activity (TE) and the
entire project.
The earliest expected completion time for a given activity is determined
by summing the expected completion time of this activity and the earliest
expected completion time of the immediate predecessor.
Rule: if two or more activities precede an activity, the one with the largest
TE is used in calculation (e.g., for activity 4, we will use TE of activity 3
but not 2 since 12 > 11).
the critical path 1,3,4,6,7,8
TE = 20
2
5
6
TE = 14
TE = 23
8
1
6
TE = 5
1
5
4
TE = 12
2
TE = 19
3
TE = 22
6
7
5
3
Fig (5-3) critical path
The critical path represents the shortest time, in which a project can be
completed. Any activity on the critical path that is delayed in completion
delays the entire project. Activities not on the critical path contain slack
time and allow the project manager some flexibility in scheduling.
PERT
Immed.
Activity Predec.
A
-B
-C
A
D
A
E
A
F
B,C
G
B,C
H
E,F
I
E,F
J
D,H
K
G,I
Optimistic
Time (Hr.)
4
1
3
4
0.5
3
1
5
2
2.5
3
Most Likely
Time (Hr.)
6
4.5
3
5
1
4
1.5
6
5
2.75
5
Pessimistic
Time (Hr.)
8
5
3
6
1.5
5
5
7
8
4.5
7
D
3
A
5
E
H
C
1
J
4
7
B
I
K
F
G
2
6
Fig (5-4) PERT Network
Activity
A
B
C
D
E
F
G
H
I
J
K
Expected Time
6
4
3
5
1
4
2
6
5
3
5
Activity ES
A
0
EF
6
LS
0
Variance
4/9
4/9
0
1/9
1/36
1/9
4/9
1/9
1
1/9
4/9
LF Slack
6
0 *critical
B
C
D
E
F
G
H
I
J
K
0
6
6
6
9
9
13
13
19
18
4
9
11
7
13
11
19
18
22
23
5
6
15
12
9
16
14
13
20
18
9
9
20
13
13
18
20
18
23
23
5
0*
9
6
0*
7
1
0*
1
0*
The estimated project completion time is the Max EF at node 7 = 23.
s2 = s2A + s2C + s2F + s2H + s2K
= 4/9 + 0 + 1/9 + 1 + 4/9
= 2
 path = 1.414
z = (24 - 23)/(24-23)/1.414 = .71
From the Standard Normal Distribution table:
P(z < .71) = .5 + .2612 = .7612
f(x)
P(T< 24) = .7612
.5000 .2612
 
Fig (5-5) Probability the project will be completed within 24 hrs
x
PERT/COST
Activity Normal Normal Crash
time
cost RS time
1
2
3
4
5
6
7
12
8
4
12
4
4
4
3000
2000
4000
50000
500
500
1500
75000
7
5
3
9
1
1
3
Allowable
Crash
crash
cost
time
5000
5
3500
3
7000
1
71000
3
1100
3
1100
3
22000
1
110700
slope
400
500
3000
7000
200
200
7000
Table (1) Time Cost data
4
2
8
1
2
7
4
1
1
2
3
4
5
4
Fig (5-4) PERT Network
6
4
R7000
R500
Project duration = 36
4
2
8
R700
12
7
4
1
12
R400
3
4
R3000
5
4
6
4
R200
R200
Fig (5-5) Project duration
R7000
R500
Project
duration = 31
Additional cost
= R2000
4
2
8
R700
12
7
4
1
7
R400
3
4
R3000
5
4
6
4
R200
R200
Fig (5-6) modified Project duration
Summary
Program evaluation and review technique (PERT) charts depict
task, duration, and dependency information. Each chart starts with an
initiation node which is the first task. Each task is represented by a node
(Activity on Node Network – AON) with lines connecting dependent
tasks.
Each task is connected to its successor tasks in this manner forming a
network of nodes and connecting lines. The chart is complete when all
final tasks come together at the completion node. When slack time exists
between the end of one task and the start of another, the usual method is
to draw a broken or dotted line between the end of the first task and the
start of the next dependent task.
PERT charts are usually drawn on ruled paper with the horizontal axis
indicating time period divisions in days, weeks, months, and so on. Many
PERT charts terminate at the major review points, such as at the end of
the analysis.
Critical Path Method (CPM) charts are similar to PERT charts and are
sometimes known as PERT/CPM. In a CPM chart, the critical path is
indicated. A critical path consists that set of dependent tasks (each
dependent on the preceding one), which together take the longest time to
complete. Tasks which fall on the critical path should be noted in some
way, so that they may be given special attention. One way is to draw
critical path tasks with a double line instead of a single line.
Tasks which fall on the critical path should receive special attention by
both the project manager and the personnel assigned to them.
The critical path for any given method may shift as the project
progresses; this can happen when tasks are completed either behind or
ahead of schedule, causing other tasks which may still be on-schedule to
fall on the new critical path.
Critical path computations are quite simple , yet they provide valuable
information that simplifies the scheduling of complex projects. The result
is that PERT-CPM techniques enjoy tremendous popularity among
practitioners in the field .The usefulness of the techniques is further
enhanced by the availability of specialized computer system for executing
,analyzing, and controlling network projects.
CPM Benefits
• Provides a graphical view of the project.
• Predicts the time required to complete the project.
• Shows which activities are critical to maintaining the schedule and
which are not.
CPM Limitations
While CPM is easy to understand and use, it does not consider the time
variations that can have a great impact on the completion time of a
complex project. CPM was developed for complex but fairly routine
projects with minimum uncertainty in the project completion times.
For less routine projects there is more uncertainty in the completion
times, and this uncertainty limits its usefulness.
Benefits of PERT
PERT is useful because it provides the following information:
• Expected project completion time.
• Probability of completion before a specified date.
• The critical path activities that directly impact the completion time.
• The activities that have slack time and that can lend resources to critical
path activities.
• Activities start and end dates.
Limitations of PERT
The following are some of PERT's limitations:
• The activity time estimates are somewhat subjective and depend on
judgment. In cases where there is little experience in performing an
activity, the numbers may be only a guess. In other cases, if the person or
group performing the activity estimates the time there may be bias in the
estimate.
• The underestimation of the project completion time due to alternate
paths becoming critical is perhaps the most serious.