Probabilistic Activity TimesProbabilistic Time Estimates

Carrine Kezia Aulia :: 102183022

• Single time estimates

• Didn’t allow for any variation

• AT treated as if they are known for certain

COMPARISON CPM AND PERTREVIEW

• Multiple time estimates

• Allow for any variation

• AT treated as probabilistic

PERT uses probabilistic activity times

CPM PERT

Approach to estimating activity times

WHAT IS PROBABILISTIC ACTIVITY TIMES?What’s it all about?

• Completion time estimates can be estimated using the

Three Time Estimate Three Time Estimate approachapproach

• In this approach, three time estimates are required for each activity

MOST LIKELY TIME (m)

THREE TIME ESTIMATES

OPTIMISTIC TIME (a)

PESSIMISTIC TIME (b)

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most frequently occur if the activity were repeated many times

the shortest possible time to complete the activity if everything went right

the longest possible time to complete the activity if everything went wrong

with THREE TIME estimates, the activity completion timecan be approximated by a BETA DISTRIBUTION

BETA DISTRIBUTION

BETA DISTRIBUTIONS CAN COME IN A VARIETY OF SHAPES :

FORMULAMEAN AND VARIANCE

a + 4m + b

6

b - a

6

2

mean (expected time)

variance σ2

t

MOST LIKELY TIME (m)

OPTIMISTIC TIME (a)

PESSIMISTIC TIME (b)

EXAMPLEA PROJECT NETWORK WITH PROBABILISTIC TIME ESTIMATE

EXAMPLEACTIVITY TIME ESTIMATES

a + 4m + b

6

b - a

6

2

t σ2

EXAMPLEACTIVITY EARLIEST AND LATEST TIMES AND SLACK

EXAMPLEACTIVITY EARLIEST AND LATEST TIMES AND SLACK

0

8

8 8

5

13

0

6

6

3

0 3

3

6 9

4

3 7

2

3 5

7

9 16

4

9 13

4

13 17

9

16 25

2516

2521

2116

169

1612

1614

95

52

9660

91

EXPECTED TIME : 25CRITICAL PATH :2-5-8-11

EXAMPLEACTIVITY EARLIEST AND LATEST TIMES AND SLACK

25WEEKS

6,89WEEKS

EXAMPLEPROBABILISTIC ANALYSIS OF THE PROJECT NETWORK

ADD ALL THE σ2 OFF THE CRITICAL PATH

SD

what does this formula means?what does these numbers mean?

EXAMPLEPROBABILISTIC ANALYSIS OF THE PROJECT NETWORK

25WEEKS

6,89WEEKS

2,62WEEKS

EXPECTED TIME

μ

σ2 σ

EXAMPLEPROBABILISTIC ANALYSIS OF THE PROJECT NETWORK

25WEEKS

EXPECTED TIME

μ

30WEEKS

PROPOSED PROJECT TIME

X WHAT IS THE PROBABILITY THAT

THE SYSTEM WILL BE READY BY THAT

TIME?

WHAT IS THE PROBABILITY THAT

THE SYSTEM WILL BE READY BY THAT

TIME?

EXAMPLEPROBABILISTIC ANALYSIS OF THE PROJECT NETWORK

Z =X – μ

σ

30WEEKS

25WEEKS

2.62

-= 1.911.91

EXAMPLEACTIVITY EARLIEST AND LATEST TIMES AND SLACK

z = 1.91

EXAMPLEACTIVITY EARLIEST AND LATEST TIMES AND SLACK

EXAMPLEACTIVITY EARLIEST AND LATEST TIMES AND SLACK

0.9719probability of completing

the project in 30 days

0.9719probability of completing

the project in 30 days

EXAMPLEACTIVITY EARLIEST AND LATEST TIMES AND SLACK

www.measuringusability.com

EXAMPLEACTIVITY EARLIEST AND LATEST TIMES AND SLACK

z = 1.91

97.19 %