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Aim: Program Evaluation and Review Technique (PERT)

�Objectives: At the end of the lesson, the students should be able to:

Construct a project network using PERT.
Determine the critical path and expected project completion time.
Discuss the importance of PERT.

Aim and Objectives

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Introduction

In general, two construction planning methods are adopted in practice by most contracting organisations. These are bar charts and networks.
Networks are usually adopted by the organisation for the purpose of providing highly detailed programming for a project. They draw attention to the activities on the programme which are on the critical path. This makes them very good for monitoring and controlling the progress of a project.
Examples of network analysis diagrams are Program Evaluation and Review Technique (PERT) and Critical Path Method (CPM).
Bar charts used for their clarity and ease of communication in conveying the basis of the programme schedule.

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Network Analysis

Networks are often presented as one of two types: as ‘arrow diagrams’ or as ‘precedence diagrams’ (Figs. 1 & 2).
The two methods essentially achieve the same goal, but with different means of depicting the information.
In this lesson, only the Program Evaluation and Review Technique (PERT) will be considered.

Figure 1. Nomenclature for compiling the Program Evaluation and Review Technique (March, 2017).

Figure 2. Nomenclature for compiling the Critical Path Method (March, 2017).

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Definition – PERT

Program Evaluation and Review Technique (PERT) is a network analysis technique used to estimate project duration when there is a high degree of uncertainty about the individual activity duration estimates.

PERT uses probabilistic time estimates.

Duration estimates based on using optimistic, most likely, and pessimistic estimates of activity durations, or a three-point estimate.
PERT attempts to address the risk associated with duration estimates by developing schedules that are more realistic.

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Definition – PERT Formula

PERT weighted average =

optimistic time + (4 X most likely time) + pessimistic time

Example: If the optimistic time = 8 days, most likely time = 10 days, and pessimistic time = 24 days

PERT weighted average =

8 + (4 X 10) + 24 = 12 days

Therefore, you would use 12 days on the network diagram instead of 10 days when using PERT.

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Worked Example

Using the information in the table below;

Find the expected duration of each activity.
Construct the project network or logic.
Find the critical path and expected project completion time.

All time in weeks.

Activity/Task	Optimistic (O)	Realistic (R)	Pessimistic (P)	PERT time t = (O + 4R + P) /6 (Expected duration)	predecessor
A	2	3	4
B	1	2	3		A
C	3	5	7		A
D	2	5	8		C
E	3	4	5		B
F	8	10	18		D
G	3	3	9		D, E
H	6	6	12		F, G

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Worked Example: Solution

Find the expected duration of each activity

Activity/Task	Optimistic (O)	Realistic (R)	Pessimistic (P)	PERT time t = (O + 4R + P) /6 (Expected duration)	predecessor
A	2	3	4	3
B	1	2	3	2	A
C	3	5	7	5	A
D	2	5	8	5	C
E	3	4	5	4	B
F	8	10	18	11	D
G	3	3	9	4	D, E
H	6	6	12	7	F, G

All time in weeks.

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Worked Example: Solution

2) Sketch the project network or logic.

Activity/Task	PERT time t = (O + 4R + P) /6 (Expected duration)	predecessor
A	3
B	2	A
C	5	A
D	5	C
E	4	B
F	11	D
G	4	D, E
H	7	F, G

All time in weeks.

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Worked Example: Solution

3) Find the critical path and expected project completion time.

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Importance – PERT

PERT employs a network visualisation to illustrate the connections between project tasks and aids managers in tackling inquiries like:
What's the projected total duration for completing the project?
When do individual activities begin and conclude?
Which activities are critical for adhering to the estimated project completion time?
To what extent can non-critical activities be postponed without impacting the overall project timeline?
Etc.

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Self-assessment Task 1 – PERT

Using the information in the table below;

Find the expected duration of each activity.
Construct the project network or logic.
Find the critical path and expected project completion time.

All time in days.

Activity/Task	Optimistic (O)	Realistic (R)	Pessimistic (P)	PERT time t = (O + 4R + P) /6 (Expected duration)	predecessor
A	12	15	18
B	6	9	12
C	9	12	15		A
D	6	9	18		B
E	18	30	36		B
F	9	12	15		A
G	36	36	42		C
H	42	48	54		D
I	6	12	18		A
J	3	6	9		H.G.E
K	3	6	9		F,J,I

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Self-assessment Task 2 – PERT

Using the information in the table below;

Find the expected duration of each activity.
Construct the project network or logic.
Find the critical path and expected project completion time.

All time in weeks.

Activity/Task	Optimistic (O)	Realistic (R)	Pessimistic (P)	PERT time t = (O + 4R + P) /6 (Expected duration)	predecessor
A	1	2	4		-
B	3	5	7		-
C	9	11	15		A
D	6	9	11		B, G
E	8	10	13		C, D
F	1	3	7		D
G	3	6	9		A
H	4	4	5		E
I	2	5	9		-
J	3	6	9		I

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References/Bibliography

March, C. (2017) Construction management – theory and practice. London: Routledge.
Morton, R. (2002) Construction UK: Introduction to the industry. Oxford: Blackwell Science.
Virginia IT Agency (2023) Program Evaluation and Review Technique (PERT). Available at: https://www.vita.virginia.gov/policy--governance/glossary/cov-itrm-glossary/p/program-evaluation-and-review-technique-pert.html#:~:text=Program%20Evaluation%20and%20Review%20Technique%20(PERT),-Definition&text=An%20event%2Doriented%20network%20analysis,a%20weighted%20average%20duration%20estimate. (Accessed: 01 November 2023).
Zornes, T. (n.d.) Critical path method (cpm). Available at: https://sixsigmastudyguide.com/critical-path-method-cpm/ (Accessed: 07 November 2023).