Q. 3 Define PERT. Prepare PERT diagram for ‘Result Day’ celebration to explain its process step-wise including all activities in detail
Course: Management Strategies in Educational Institutions
Course Code 8615
Topics
- Define PERT
- Explain the process of PERT step-wise in detail
- Prepare PERT diagram For "Result Day" celebration
- Identify the specific activities and milestones, Determine the proper sequence of the activities,Construct a network diagram,Estimate the time required for each activity.
Answer:
Complex projects require a series of
activities, some of which must be performed sequentially and others that can be
performed in parallel with other activities. This collection of series and
parallel tasks can be modeled as a network.
In 1957 the Critical Path Method
(CPM) was developed as a network model for project management. CPM is a
deterministic method that uses a fixed time estimate for each activity. 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.
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 originally was an activity on arc network, in which the
activities are represented on the lines and milestones on the nodes. Over time,
some people began to use PERT as an activity on node network. For this
discussion, we will use the original form of activity on arc.
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:
I.
Identify the specific activities and milestones.
II.
Determine the proper sequence of the activities.
III.
Construct a network diagram.
IV.
Estimate the time required for each activity.
V.
Determine the critical path.
VI.
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. 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 Activity Sequence
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 the Network Diagram
Using the activity sequence
information, a network diagram can be drawn showing the sequence of the serial
and parallel activities. For the original activity-on-arc model, the activities
are depicted by arrowed lines and milestones are depicted by circles or
"bubbles". If done manually, several drafts may be required to correctly
portray the relationships among activities. Software packages simplify this
step by automatically converting tabular activity information into a network
diagram.
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 - generally the shortest time in which
the activity can be completed. It is common practice to specify optimistic
times to be three standard deviations from the mean so that there is
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 times, then there are six standard deviations
between them, so the variances given by:
[ ( Pessimistic - Optimistic ) / 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 calendar 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 earliest start and finish times
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
assuming a normal probability distribution for the critical path. The normal
distribution assumption holds if the number of activities in the path is large
enough for the central limit theorem to be applied.
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.
No comments:
Post a Comment
If you have any question related to children education, teacher education, school administration or any question related to education field do not hesitate asking. I will try my best to answer. Thanks.