PERT Charts
Prepared by: Michael Palazzo
What are PERT Charts?
O PERT stands for Program
Evaluation and Review Technique
O To understand what a PERT chart
is, we must first learn the Critical
Path Method (CPM)
CPM
O Developed as a network model for
project management
O Uses a fixed time estimate for each
activity
O Easy to understand but does not
account for time variations of
activities
What is PERT?
O Developed in late 1950’s
O A network model that allows for
randomness in activity completion times
O Has potential to reduce time and cost to
complete a project
Network Diagrams
O PERT Charts use network diagrams
O Activities and milestones of a project are
represented by arcs and nodes on a model
O PERT was originally Activity-on-Arc diagram
O Some now use Activity-on-Node
Arc vs. Node
Activity-on-arc
network:
Activity-on-node
network:
Example of a PERT Chart
6 Steps
1. Identify
5. Determine Critical
Path
2. Determine Activity
Sequence
3. Construct
4. Estimate
6. Update
Identify/Determine Activity
Sequence
O Identify Activities and Milestones:
O Activities are tasks
O Milestones mark beginning and end of
activities
O Determine Activity Sequence:
O Sequence is evident for some
O Others require more analysis
Construct
O Construct the Network Diagram:
O Create diagram with activity sequence info
O For activity-on-arc model, activities are
arrowed lines and milestones are circles
O Software exists to simplify this step
Estimate
O Estimate Activity Times:
O Weeks are commonly used as
unit of time
O PERT is able to deal with
uncertainty in activity
completion times
O Each activity in model includes
three time estimates
Estimate Continued…
O Optimistic Time:
O Shortest time activity can be completed
O Most Likely Time:
O Completion time with highest probability
O Pessimistic Time:
O Longest time the activity might require
Determine Critical Path
O Critical path is longest path in project
O Determined by adding the times for
activities in each sequence
O By accelerating activities on critical
path you decrease total project time
Update
O Update as Project Progresses:
O Make adjustments to PERT chart as
project continues
O Resources may need to be added to stay
on schedule if there are delays
Benefits of PERT
O Gives expected project completion
time
O Provides probability of completion
before a date
O Shows critical path activities
Benefits Continued…
O Provides activity start and end dates
O Shows activities that have slack time
Limitations of PERT
O The activity time estimates are
subjective
O PERT assumes a beta
distribution for its time
estimates; actual distribution
may be different
Limitations Continued…
O Consistently underestimates the expected
project completion time
O PERT assumes probability distribution of
project completion time is same as critical path
O If delayed, other paths can become critical
path
References
O Pert Charts:
http://www.netmba.com/operations/project/pert/
O More Information on CPM/CPA:
http://www.mindtools.com/critpath.html
O PERT Chart Images:
http://en.wikipedia.org/wiki/Program_Evaluation_and_
Review_Technique
http://cpmtutor.com/c05/fp-dummies.html
http://cnx.org/content/m32170/latest/
Thank you for your
attention!