Download - PERT Charts
PERT Charts
Prepared by: Michael Palazzo
What are PERT Charts?OPERT stands for Program
Evaluation and Review Technique
OTo understand what a PERT chart is, we must first learn the Critical Path Method (CPM)
CPMODeveloped as a network model
for project managementOUses a fixed time estimate for
each activityOEasy to understand but does
not account for time variations of activities
What is PERT?ODeveloped in late 1950’s
OA network model that allows for randomness in activity completion times
OHas potential to reduce time and cost to complete a project
Network DiagramsOPERT Charts use network diagrams
OActivities and milestones of a project are represented by arcs and nodes on a model
OPERT was originally Activity-on-Arc diagram
OSome now use Activity-on-Node
Arc vs. NodeActivity-on-
arc network:
Activity-on-node network:
Example of a PERT Chart
6 Steps1. Identify
2. Determine Activity Sequence
3. Construct
4. Estimate5. Determine
Critical Path
6. Update
Identify/Determine Activity Sequence
O Identify Activities and Milestones:O Activities are tasksO Milestones mark beginning and end
of activities
ODetermine Activity Sequence:O Sequence is evident for someO Others require more analysis
ConstructOConstruct 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
EstimateOEstimate 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…OOptimistic Time:
O Shortest time activity can be completed
OMost Likely Time:O Completion time with highest probability
OPessimistic Time:O Longest time the activity might require
Determine Critical PathOCritical path is longest path in
project
ODetermined by adding the times for activities in each sequence
OBy accelerating activities on critical path you decrease total project time
UpdateOUpdate 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 PERTOGives expected project
completion time
OProvides probability of completion before a date
OShows critical path activities
Benefits Continued…
OProvides activity start and end dates
OShows activities that have slack time
Limitations of PERTOThe activity time estimates
are subjective
OPERT assumes a beta distribution for its time estimates; actual distribution may be different
Limitations Continued…
OConsistently underestimates the expected project completion timeO PERT assumes probability distribution
of project completion time is same as critical path
O If delayed, other paths can become critical path
ReferencesO 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.htmlhttp://cnx.org/content/m32170/latest/
Thank you for your attention!