Instructor S Resource Manual

INSTRUCTOR’S RESOURCE MANUAL

CHAPTER NINE

Project Scheduling:

Networks, Duration Estimation, and Critical Path

To Accompany

PROJECT MANAGEMENT:

Achieving Competitive Advantage

Jeffrey K. Pinto

CHAPTER NINE

PROJECT FOCUS – The Spallation Neutron Source Project

INTRODUCTION

9.1 PROJECT SCHEDULING

9.2 KEY SCHEDULING TERMINOLOGY

9.3 DEVELOPING A NETWORK

Labeling Nodes

Serial Activities

Concurrent Activities

Burst Activities

Merge Activities

9.4 DURATION ESTIMATION

9.5 CONSTRUCTING THE CRITICAL PATH

Calculating the Network

The Forward Pass

The Backward Pass

Laddering Activities

Hammock Activities

Steps to Reduce the Critical Path

Project Management Research in Brief – Software Development Delays and Solutions

Summary

Key Terms

Solved Problems

Discussion Questions

Problems

Internet Exercises

MSProject Exercises

PMP Certification Sample Questions

Bibliography

TRANSPARENCIES

9.1 RULES FOR DEVELOPING ACTIVITY NETWORKS

1. Some determination of activity precedence ordering must be done prior to creating the network.

2. Network diagrams usually flow from left to right.

3. An activity cannot begin until all preceding connected activities have been completed.

4. Arrows on networks indicate precedence and logical flow. Arrows can cross over each other, although it is helpful for clarity’s sake to limit this effect when possible.

5. Each activity should have a unique identifier associated with it (number, letter, code, etc.).

6. Looping, or recycling through activities, is not permitted.

7. Although not required, it is common to start a project from a single beginning node. A single node point also is typically used as a project end indicator.

9.2 LABELS FOR ACTIVITY NODE

9.3 PROJECT ACTIVITIES LINKED IN SERIES

9.4 ACTIVITIES LINKED IN PARALLEL (CONCURRENT)

9.5 MERGE ACTIVITIES

9.6 BURST ACTIVITIES

9.7 EXAMPLE OF CREATING A PROJECT ACTIVITY NETWORK

Information for Network Construction

Name: Project Delta

Activity Description Predecessors

A Contract signing None

B Questionnaire design A

C Target market ID A

D Survey sample B, C

E Develop presentation B

F Analyze results D

G Demographic analysis C

H Presentation to client E, F, G

9.8 ACTIVITY NETWORK FOR EXAMPLE

9.9 ACTIVITY DURATION ESTIMATION – BETA DISTRIBUTION

ESTIMATED TIME FORMULA

TE = A + 4(B) + C

WHERE:

A = MOST OPTIMISTIC TIME

B = MOST LIKELY TIME

C = MOST PESSIMISTIC TIME
9.10 CONSTRUCTING THE CRITICAL PATH

INFORMATION FOR PROJECT DELTA

Activity Description Predecessors Estimated Duration

A Contract signing None 5

B Questionnaire design A 5

C Target market ID A 6

D Survey sample B, C 13

E Develop presentation B 6

F Analyze results D 4

G Demographic analysis C 9

H Presentation to client E, F, G 2

9.10 (Con’d)

Partial Project Activity Network with Task Durations

RULES WHEN USING THE FORWARD PASS

1. Add all activity times along each path as we move through the network (ES + Dur = EF),

2. Carry the EF time to the activity nodes immediately succeeding the recently completed node. That EF becomes the ES of the next node, unless the succeeding node is a merge point.

3. At a merge point, the largest preceding EF becomes the ES for that node.

9.12 ACTIVITY NETWORK WITH FORWARD PASS

9.13 RULES FOR USING THE BACKWARD PASS

1. Subtract activity times along each path as you move through the network (LF – Dur = LS),

2. Carry back the LS time to the activity nodes immediately preceding the successor node. That LS becomes the LF of the next node, unless the preceding node is a burst point.

3. In the case of a burst point, the smallest succeeding LS becomes the LF for that node.

ACTIVITY NETWORK WITH BACKWARD PASS

9.15 COMPLETED ACTIVITY NETWORK WITH CRITICAL PATH AND ACTIVITY SLACK TIMES IDENTIFIED

Critical Path is indicated in bold

9.16 ACTIVITY NETWORK DEMONSTRATING LADDERING TECHNIQUE

9.17 NETWORK DEMONSTRATING HAMMOCK ACTIVITY

9.18 STEPS TO REDUCE THE CRITICAL PATH

1. ELIMINATE TASKS ON THE CRITICAL PATH

2. REPLAN SERIAL PATHS TO BE PARALLEL

3. OVERLAP SEQUENTIAL TASKS

4. SHORTEN THE DURATION ON CRITICAL PATH ACTIVITIES

5. SHORTEN EARLY TASKS

6. SHORTEN LONGEST TASKS

7. SHORTEN EASIEST TASKS

8. SHORTEN TASKS THAT COST THE LEAST TO SPEED UP

DISCUSSION QUESTIONS

1. Define the following terms:

a. Path: group of activities sequenced by relationship through project network logic

b. Activity: any piece of work that will be performed during the project which has an expected time and cost for completion

c. Early start: the earliest possible date upon which an uncompleted activity or project can start based on sequencing and scheduling constraints

d. Early finish: the earliest possible date upon which an uncompleted activity or project can be completed

e. Late start: the latest date an activity may start without delaying other project milestones or the project’s expected completion date

f. Late finish: the latest date an activity may end without delaying other project milestones or the project’s expected completion date

g. Forward pass: a process that works forward though the project network to determine the earliest start and earliest finish time for an activity

h. Backward pass: a process that works backwards through the project network to calculate the latest finish times for an uncompleted activity

i. Node: a convergence point of dependent paths in a network

j. AON: Activity on Node; a method of logic that determines activity networks in which a node depicts an activity and arrows indicate sequencing between nodes

k. Float: a calculation which determines the amount of time an activity can be delayed from its earliest start date without delaying the project’s completion date l.

l. Critical Path: the path through the project network having the least amount of float time and the longest time duration

m. PERT: Project Evaluation and Review Technique; a network analysis system based on events and probability used when activities and their duration are difficult to define

2. Distinguish between serial activities and concurrent activities. Why do we seek to use concurrent activities as a way to shorten a project’s length?

Serial activities begin with the first step and proceeding to subsequent steps one at a time sequentially until the project is completed. Serial activities must be completed in order and one at a time. Therefore, step 2 can not begin until step1 has been completed, and so on. Concurrent activities allow more than one activity to be performed during the same time period. This means step 1 may still be in progress when step 2 is started. Project teams seek out concurrent activities because they allow multiple phases of the project to be progressing simultaneously. Time savings occur from several activities being completed at the same time and delays in one step do not created delays in other concurrent activities. This method allows activities to work more independently which means the project can progress at a faster pace.

3. List three methods for deriving duration estimates for project activities. What are the strengths and weaknesses associated with each method?

One method for deriving time estimates is past experience. This method is beneficial in that it is easy and uses past examples of similar activities to predict future time estimates. However, it is limited in that estimates can be distorted by extenuating circumstances, changes in time and conditions, and information obsolescence. Another method uses expert opinion. Again, the approach is simple to use and draws on experience and knowledge of experts. The shortcomings here involve potential inadequacy of staff (at least relative to the expert giving the opinion) and project-specific complications. A third method employs mathematical derivations. This approach is more objective and allows multiple estimates (based on best, most likely and worst case analysis). The weaknesses of this method are that it is slightly more difficult to use and it disregards past failures (a.k.a. lessons learned).

4. In your opinion, what are the chief benefits and drawbacks of using beta distribution calculations (based on PERT techniques) to derive activity duration estimates?

Beta distribution allows for the likelihood that optimistic and pessimistic times will not be symmetrical. By including realistic estimates of pessimistic and optimistic durations beta distribution creates a more accurate distribution of alternative duration times. One drawback to this method is that it is relies on estimates of pessimistic and optimistic time estimates which not be reliable. There has also been some debate related to how the time estimates in this method should be calculated and/or interpreted.

5. “The shortest total length of a project is determined by the longest path through the network.” Explain the concept behind this statement. Why does the longest path determine the shortest project length?

This is based on the concept of critical path. The critical path combines the project activity network (the order to be followed for start/completion of activities) and the estimated time duration of activities in the sequence (how long each activity will take to complete) to determine the length of time required to complete the project. The longest path of sequential events is used to establish the project’s duration because the events in the path must be performed one after another. Adding the duration times of activities in the critical path will result in the shortest project length (i.e. how long it will take to perform required serial activities).

6. The float associated with each project task can only be derived following the completion of the forward and backward passes. Explain why this is true.

The forward pass establishes the earliest time that activities in the network can begin and end. The backward pass determines the latest time activities in the network can begin and end. Float time is the difference between the task’s latest and earliest end time (or the task’s latest and earliest start time). Hence, float cannot be calculated until the forward and backward pass have been completed.

PROBLEMS

1. Consider a project, such as moving to a new neighborhood, completing a long-term school assignment, or even cleaning your bedroom. Develop a set of activities necessary to accomplish that project and then order them in a precedence manner to create sequential logic. Explain and defend the number of steps you identified and the order in which you placed those steps for best completion of the project.

SOLUTION:

This problem is intended to get students thinking sequentially; that is, developing first a set of activities or tasks and then applying some informal sequential logic to the order so that they can become familiar with concepts such as predecessor and successor activities. The key is to challenge their sequencing to determine if they have correctly identified both the necessary activities and the order in which they should be considered.

2. What is the time estimate of the following activity in which the optimistic estimate is 4 days, pessimistic is 12 days, and most likely is 5 days? Show your work.

SOLUTION:

Using the Beta distribution for probabilistic estimation, the formula is given as:

TE = (a + 4m + b)/6

Where:

TE = Estimated time for activity

a = most optimistic time to complete the activity

m = most likely time to complete the activity, the mode of the distribution

b = most pessimistic time to complete the activity

The solution to this problem is:

TE = (4 + 4(5) + 12)/6, or

= 6

3. Consider the following project tasks and their identified best, likely, and worst case estimates of task duration. Assume the organization you work for computes TE based on the standard formula. Calculate the TE for each of the following tasks (round to the nearest integer):

Activity Best Likely Worst TE

A 5 5 20

B 3 5 9

C 7 21 26

D 4 4 4

E 10 20 44

F 3 15 15

G 6 9 11

H 32 44 75

I 12 17 31

J 2 8 10

SOLUTION:

Using the Beta distribution for probabilistic estimation, the formula is given as:

TE = (a + 4m + b)/6

Where:

TE = Estimated time for activity

a = most optimistic time to complete the activity

m = most likely time to complete the activity, the mode of the distribution

b = most pessimistic time to complete the activity

Activity Best Likely Worst TE

A 5 5 20 8

B 3 5 9 5

C 7 21 26 20

D 4 4 4 4

E 10 20 44 22

F 3 15 15 13

G 6 9 11 9

H 32 44 75 47

I 12 17 31 19

J 2 8 10 7

4. Construct a network activity diagram based on the following information:

Activity Preceding activities

A -

B -

C A

D B, C

E B

F C, D

G E

H F

I G, H

SOLUTION:

5. Consider a project with the following information:

Activity Duration Predecessors

A 3 --

B 5 A

C 7 A

D 3 B, C

E 5 B

F 4 D

G 2 C

H 5 E, F, G

Activity Duration ES EF LS LF Slack

A 3 0 3 0 3 --

B 5 3 8 5 10 2

C 7 3 10 3 10 --

D 3 10 13 10 13 --

E 5 8 13 12 17 4

F 4 13 17 13 17 --

G 2 10 12 15 17 5

H 5 17 22 17 22 --

A. Construct the project activity network using AON methodology and label each node.

B. Identify the critical path and other paths through the network.

Solution:

The Critical Path is: A – C – D – F - H

Alternative paths are: A – B – E – H

A – B – D – F – H

A – C – G – H

6. An advertising project manager has developed a program for a new advertising campaign. In addition, the manager has gathered the time information for each activity, as shown in the table below.