DIFFERENCE BETWEEN PERT & CPM

DIFFERENCE

PERT

• PERT (Programme Evaluation & Review Technique) is event oriented.

• PERT activities are shown as a network of precedence relationships using activity-on-arrow network construction

• PERT treats activity time as a random variable

• PERT focuses exclusively on the time variable

CPM

• CPM (Critical Path Method) is activity oriented.

• CPM activities are shown as a network of precedence relationships using activity-on-node network construction

• CPM requires a single deterministic time value for each activity.

• CPM includes the analysis of the Time/Cost Trade-off.

PERT

• PERT is a probabilistic Model. It uses three estimates of the activity time- optimistic, pessimistic and most Likely with a view to take into account time uncertainty.

• PERT is primarily concerned with time. It helps the manager to schedule and co-ordinate various activities so that the project can be completed on schedule time.

CPM

• CPM is a deterministic model i.e. it dose not take into account the uncertainties. Involved in the estimation of time for execution of a job or an activity. It completelyIgnores the probabilistic element of the problem.

• CPM place dual emphasis on time and cost and evaluate the trade off between project Cost and project time. 

PERT

• Suitable for repetitive projects

• Demarcate critical and noncritical activities

• determined on the basis of slack

• Suitable for defense• Dummies are not required• Crashing is not applicable

CPM

• Suitable for new projects • Does not demarcate

between critical and & noncritical activities

• Critical path is determined on the basis of float

• Suitable for industrial project settings

• Dummies are compulsory• Crashing is applicable

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

CPM Example• Critical Path

a, 6a, 6

f, 15f, 15

b, 8b, 8

c, 5c, 5

e, 9e, 9

d, 13d, 13

g, 17g, 17 h, 9h, 9

i, 6i, 6

j, 12j, 12

darla/smbs/vit

PERT • 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:– pessimistic time (tp ) - the time the activity would take if

things did not go well– most likely time (tm ) - the consensus best estimate of the

activity’s duration– optimistic time (to ) - the time the activity would take if

things did go well

Mean (expected time): te =tp + 4 tm + to

6

Variance: Vt =2 =tp - to

6

2

tp-to

6

PERT analysis

• 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

Z = x -

where = tp = project mean time

= project standard mean time

x = (proposed ) specified time

darla/smbs/vit 10

AOA Project Network for House

32 0

1

31 1

11 2 4 6 7

3

5

Lay foundation

Design house and obtain financing

Order and receive materials

Dummy

Finish work

Select carpet

Select paint

Build house

AON Project Network for House

13

22

43

31 5

1

61

71Start

Design house and obtain financing

Order and receive materials

Select paintSelect carpet

Lay foundations Build house

Finish work

THANKZ………