Milestone 2
Decision Trees Using TreePlan 16
16.1 TREEPLAN OVERVIEW TreePlan is a decision tree add-in for Microsoft Excel 2007–2013 (Windows) and Microsoft Excel 2011 (Macintosh).
TreePlan helps you build a decision tree diagram in an Excel worksheet using dialog boxes. Decision trees are useful for analyzing sequential decision problems under uncertainty. Your decision tree model may include various controllable alternatives (e.g., whether to introduce a new product, whether to bid on a new project) and uncontrollable uncertainties (e.g., possible demand for a product, whether you're awarded a contract), arranged in chronological order. TreePlan automatically includes formulas for summing cash flows to obtain outcome values and for calculating rollback values for determining the optimal strategy.
To use TreePlan, you (1) open a new worksheet, (2) press Ctrl+Shift+T (or Option+Cmd+T) to build a new decision tree diagram, (3) select a node to change the structure of your decision tree, (4) enter branch names, cash flows, and probabilities, and (5) determine the optimal strategy from TreePlan's results.
All of TreePlan’s functionality, including its built-in help, is a part of the TreePlan XLAM file. There is no separate setup file or help file. When you use TreePlan on a Windows computer, it does not create any Windows Registry entries (although Excel may use such entries to keep track of its add-ins).
16.2 BUILDING A DECISION TREE IN TREEPLAN With Windows Excel 2007 & 2010 & 2013, you can start TreePlan either by choosing Add-ins > TreePlan Decision Tree or by pressing Ctrl+Shift+T (hold down the Ctrl and Shift keys and press T).
With Mac Excel 2011, you can start TreePlan either by choosing Tools > TreePlan Decision Tree from the menu or by pressing Option+Cmd+T (hold down the Option and Command keys and press T).
If the worksheet doesn't have a decision tree, TreePlan prompts you with a dialog box with three options; choose New Tree to begin a new tree. TreePlan draws a default initial decision tree with its upper left corner at the selected cell. For example, the figure below shows the initial tree when cell C3 is selected before creating the new tree. (Note that TreePlan writes over existing values in
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196 Chapter 16 Decision Trees Using TreePlan
16.4 TREEPLAN INPUTS AND FORMULAS
Figure 16.7 Influence Chart of TreePlan Inputs and Formulas
Figure 16.8 Explanation of Formulas
16.5 STEP-BY-STEP TREEPLAN TUTORIAL A decision tree can be used as a model for a sequential decision problems under uncertainty. A decision tree describes graphically the decisions to be made, the events that may occur, and the outcomes associated with combinations of decisions and events. Probabilities are assigned to the events, and values are determined for each outcome. A major goal of the analysis is to determine the best decisions.
Decision tree models include such concepts as nodes, branches, terminal values, strategy, payoff distribution, certain equivalent, and the rollback method. The following problem illustrates the basic concepts.
Branch Inputs Cell Formulas Defined Name
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Optional
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Probability
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Event Node Rollback Value
Decision Node Choice Indicator
Decision Node Rollback Value
RT (Risk Tolerance)
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Endpoint Value at Terminal Node
SUM of branch cash flows
Rollback Value at Event Node
IF probabilities SUM to approximately one, then SUM the products of probabilities times subsequent rollback values
Rollback Value at Decision Node
MAX or MIN of subsequent rollback values
Choice Indicator at Decision Node
Nested IF functions
16.5 Step-by-Step TreePlan Tutorial 197
DriveTek Problem
DriveTek Research Institute discovers that a computer company wants a new storage device for a proposed new computer system. Since the computer company does not have research people available to develop the new storage device, it will subcontract the development to an independent research firm. The computer company has offered a fee of $250,000 for the best proposal for developing the new storage device. The contract will go to the firm with the best technical plan and the highest reputation for technical competence.
DriveTek Research Institute wants to enter the competition. Management estimates a cost of $50,000 to prepare a proposal with a fifty-fifty chance of winning the contract.
However, DriveTek's engineers are not sure about how they will develop the storage device if they are awarded the contract. Three alternative approaches can be tried. The first approach is a mechanical method with a cost of $120,000, and the engineers are certain they can develop a successful model with this approach. A second approach involves electronic components. The engineers estimate that the electronic approach will cost only $50,000 to develop a model of the storage device, but with only a 50 percent chance of satisfactory results. A third approach uses magnetic components; this costs $80,000, with a 70 percent chance of success.
DriveTek Research can work on only one approach at a time and has time to try only two approaches. If it tries either the magnetic or electronic method and the attempt fails, the second choice must be the mechanical method to guarantee a successful model.
The management of DriveTek Research needs help in incorporating this information into a decision to proceed or not.
[Source: The storage device example is adapted from Spurr and Bonini, Statistical Analysis for Business Decisions, Irwin.]
Nodes and Branches
Decision trees have three kinds of nodes and two kinds of branches. A decision node is a point where a choice must be made; it is shown as a square. The branches extending from a decision node are decision branches, each branch representing one of the possible alternatives or courses of action available at that point. The set of alternatives must be mutually exclusive (if one is chosen, the others cannot be chosen) and collectively exhaustive (all possible alternatives must be included in the set).
There are two major decisions in the DriveTek problem. First, the company must decide whether or not to prepare a proposal. Second, if it prepares a proposal and is awarded the contract, it must decide which of the three approaches to try to satisfy the contract.
An event node is a point where uncertainty is resolved (a point where the decision maker learns about the occurrence of an event). An event node, sometimes called a "chance node," is shown as a circle. The event set consists of the event branches extending from an event node, each branch representing one of the possible events that may occur at that point. The set of events must be mutually exclusive (if one occurs, the others cannot occur) and collectively exhaustive (all possible events must be included in the set). Each event is assigned a subjective probability; the sum of probabilities for the events in a set must equal one.
The three sources of uncertainty in the DriveTek problem are: whether it is awarded the contract or not, whether the electronic approach succeeds or fails, and whether the magnetic approach succeeds or fails.
198 Chapter 16 Decision Trees Using TreePlan
In general, decision nodes and branches represent the controllable factors in a decision problem; event nodes and branches represent uncontrollable factors.
Decision nodes and event nodes are arranged in order of subjective chronology. For example, the position of an event node corresponds to the time when the decision maker learns the outcome of the event (not necessarily when the event occurs).
The third kind of node is a terminal node, representing the final result of a combination of decisions and events. Terminal nodes are the endpoints of a decision tree, shown as the end of a branch on hand-drawn diagrams and as a triangle on computer-generated diagrams.
The following table shows the three kinds of nodes and two kinds of branches used to represent a decision tree.
Figure 16.9 Nodes and Symbols Type of Node Written Symbol Computer Symbol Node Successor Decision square square decision branches Event circle circle event branches Terminal endpoint triangle or bar terminal value
Terminal Values
Each terminal node has an associated terminal value, sometimes called a payoff value, outcome value, or endpoint value. Each terminal value measures the result of a scenario: the sequence of decisions and events on a unique path leading from the initial decision node to a specific terminal node.
To determine the terminal value, one approach assigns a cash flow value to each decision branch and event branch and then sum the cash flow values on the branches leading to a terminal node to determine the terminal value. In the DriveTek problem, there are distinct cash flows associated with many of the decision and event branches. Some problems require a more elaborate value model to determine the terminal values.
The following diagram shows the arrangement of branch names, probabilities, and cash flow values on an unsolved tree.
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16.5 Step-by-Step TreePlan Tutorial 201
Figure 16.15 Initial Event Branches
5. Select cell H2, and enter Awarded contract. Select cell H4, and enter 250000. Select cell H7, and enter Not awarded contract.
Figure 16.16 Event Branches With Names and Cash Flow
6. Select cell J3. Press Ctrl+Shift+T. In the TreePlan Terminal Node dialog box, select Change To Decision Node, select Three Branches, and click OK. The tree is redrawn.
1 2 3 4 5 6 7 8 9 10 11 12 13 14
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202 Chapter 16 Decision Trees Using TreePlan
Figure 16.17 Subsequent Decision Branches
7. Select cell L2, and enter Use mechanical method. Select cell L4, and enter –120000. Select cell L7, and enter Try electronic method. Select cell L9, and enter –50000. Select cell L12, and enter Try magnetic method. Select cell L14, and enter –80000.
Figure 16.18 Subsequent Decision Branches With Names and Cash Flows
8. Select cell N8. Press Ctrl+Shift+T. In the TreePlan Terminal Node dialog box, select Change To Event Node, select Two Branches, and click OK. The tree is redrawn.
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
A B C D E F G H I J K L M N O
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16.5 Step-by-Step TreePlan Tutorial 203
Figure 16.19 Branches for Electronic Method Uncertainty
9. Select cell P7, and enter Electronic success. Select cell P12, and enter Electronic failure. Select cell P14, and enter –120000.
Figure 16.20 Branch Names and Cash Flows for Electronic Method Uncertainty
10. Select cell N18. Press Ctrl+Shift+T. In the TreePlan Terminal Node dialog box, select Change To Event Node, select Two Branches, and click OK. The tree is redrawn.
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
A B C D E F G H I J K L M N O P Q R S
Use mechanical method 80000
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1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
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204 Chapter 16 Decision Trees Using TreePlan
Figure 16.21 Branches for Magnetic Method Uncertainty
11. Select cell P16, and enter .7. Select cell P17, and enter Magnetic success. Select cell P21, and enter .3. Select cell P22, and enter Magnetic failure. Select cell P24, and enter –120000.
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
A B C D E F G H I J K L M N O P Q R S
Use mechanical method 80000
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16.5 Step-by-Step TreePlan Tutorial 205
Figure 16.22 Complete Diagram Before Formatting
12. Double-click the sheet tab (or right-click the sheet tab and choose Rename from the shortcut menu), and enter Original. Save the workbook.
Interpreting the Results
The $30,000 terminal value on the far right of the diagram in cell S13 is associated with the following scenario:
Figure 16.23 Evaluation of a Scenario Branch Type Branch Name Cash Flow Decision Prepare proposal –$50,000 Event Awarded contract $250,000 Decision Try electronic method –$50,000 Event Electronic failure (Use mechanical method) –$120,000
Terminal value $30,000
TreePlan put the formula =SUM(P14,L11,H12,D20) into cell S13 for determining the terminal value.
Other formulas, called rollback formulas, are in cells below and to the left of each node. These formulas are used to determine the optimal choice at each decision node.
In cell B26, a formula displays 1, indicating that the first branch is the optimal choice. Thus, the initial choice is to prepare the proposal. In cell J11, a formula displays 2, indicating that the
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
A B C D E F G H I J K L M N O P Q R S
Use mechanical method 80000
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208 Chapter 16 Decision Trees Using TreePlan
Figure 16.26 Complete DriveTek Decision Tree
18. Double-click the Original (2) sheet tab (or right-click the sheet tab and choose Rename from the shortcut menu), and enter Formatted. Save the workbook.
Displaying Model Inputs
When you build a decision tree model, you may want to discuss the model and its assumptions with co-workers or a client. For such communication it may be preferable to hide the results of formulas that show rollback values and decision node choices. The following steps show how to display only the model inputs.
19. From the Edit menu, choose Move or Copy Sheet (or right-click the sheet tab and choose Move Or Copy from the shortcut menu). In the lower left corner of the Move Or Copy dialog box, check the Create A Copy box, and click OK.
20. On sheet Formatted (2), select cell B1. Press Ctrl+Shift+T. In the TreePlan Select dialog box, verify that the option button for Columns with Nodes is selected, and click OK. With all node columns selected, choose Format > Cells > Number or Home > Format > Format Cells > Number. In the Category list box, select Custom. Select the entry in the Type edit box, and type ;;; (three semicolons). Click OK.
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34
A B C D E F G H I J K L M N O P Q R S
Use mechanical method $80,000
-$120,000 $80,000
0.5 Electronic success
$150,000 0.5 Try electronic method $0 $150,000 Awarded contract
2 -$50,000 $90,000 0.5 $250,000 $90,000 Electronic failure
$30,000 -$120,000 $30,000
0.7 Magnetic success
Prepare proposal $120,000 Try magnetic method $0 $120,000
-$50,000 $20,000 -$80,000 $84,000 0.3
Magnetic failure $0
-$120,000 $0
1 0.5 $20,000 Not awarded contract
-$50,000 $0 -$50,000
Don't prepare proposal $0
$0 $0
F
E se va do th fo fo
P
igure 16.27 Ex
xplanation: A eparated by sem alues, and text, oes not display he cell, but its r ormat without h ormats are save
21. Select c option rollbac Cells > list box
22. Double from th
Printing the
23. In the N
24. To prin & 2010 Button tab; for option Header approp
xcel Format Ce
custom numbe micolons, and t , in that order. y positive numb result is not dis having to enter ed with the wor
cell A27. Press button for Cell k values select
> Number. In th x, and select th
e-click the Form he shortcut men
e Tree Diag
Name Box list
nt the tree diagr 0 & 2013, choo or File > Print
r Orientation cl button for Fit T
r list box select riate headers a
ells Dialog Box
er format has fo they define the When you spe bers, negative n splayed. Later, r the formula a rkbook unless
s Ctrl+Shift+T ls with Rollbac ted, choose For he Category lis e three-semico
matted (2) shee nu), and enter M
gram
box, select Tre
ram from Exce ose Page Layou t Preview > Pa lick the option To 1 Page Wid t None, and in and footers). Cl
x
our sections of e formats for po ecify three sem numbers, zero if you want to gain. Editing a you explicitly
. In the TreePl ck EVs/CEs is rmat > Cells > st box, select C olon entry. Clic
et tab (or right- Model Inputs
eeDiagram (or
el, with the tree ut > Print Area ge Setup. In th button for Lan
de By 1 Page T the Footer list lick the Sheet t
16.5 Step-by-S
f format codes. ositive number
micolons withou values, or text
o display the re an existing form delete a forma
lan Select dialo selected, and c Number or Ho
Custom. Scroll ck OK.
-click the sheet . Save the wor
select cells A1
e diagram rang a > Set Print Ar he Page Setup d ndscape, and fo Tall. Click the H
box select Non tab; clear the c
Step TreePlan Tu
The sections a rs, negative num ut format codes t. The formula esult, you can c mat does not de at.
og box, verify t click OK. With ome > Format to the bottom o
t tab and choos rkbook.
1:S34).
ge selected, in E rea. Then choo dialog box, clic or Scaling click Header/Footer ne (or select ot
check box for G
Tutorial 209
are mbers, zero s, Excel remains in
change the elete it. All
that the h all > Format of the Type
se Rename
Excel 2007 ose Office ck the Page k the tab; in the
ther Gridlines,
210 Chapter 16 Decision Trees Using TreePlan
and clear the check box for Row And Column Headings. Click OK. Choose File > Print and click OK.
25. To print the tree diagram from Word, clear the check boxes for Gridlines and for Row And Column Headings on Excel’s Page Setup dialog box Sheet tab. Select the tree diagram range. In Excel 2007 & 2010 & 2013, choose Home > Paste > As Picture > Copy as Picture. In the Copy Picture dialog box, click the option button As Shown When Printed, and click OK. In Word select the location where you want to paste the tree diagram and choose Edit > Paste.
Figure 16.28 DriveTek Without Rollback Values
Alternative Model
If you want to emphasize that the time constraint forces DriveTek to use the mechanical approach if they try either of the uncertain approaches and experience a failure, you can change the terminal nodes in cells R13 and R23 to decision nodes, each with a single branch.
Use mechanical method $80,000
-$120,000
0.5 Electronic success
$150,000 0.5 Try electronic method $0 Awarded contract
-$50,000 0.5 $250,000 Electronic failure
$30,000 -$120,000
0.7 Magnetic success
Prepare proposal $120,000 Try magnetic method $0
-$50,000 -$80,000 0.3
Magnetic failure $0
-$120,000
0.5 Not awarded contract
-$50,000 $0
Don't prepare proposal $0
$0
F
1 Tr ev ut fo
F
Fo an ex
Tr fu w R co
igure 16.29 Al
6.6 EXPO reePlan's defau vent node and m tilities in TreeP ormulas for com
igure 16.30 Tr
or the Maximiz nd CE = -LN(( xponential utili
reePlan uses th unction. The na
worksheet when RT=999999999 ommand.
Prepare
-$50,000
Don't pre
$0
lternative Driv
ONENTIA ult is to rollbac maximum of s Plan's Options mputing the uti
reePlan Option
ze option with A-EU)/B)*RT ity, the formula
he name RT to ames A and B d n you choose to 999. You can c
0.5 Awa
$250
proposal
0
0.5 Not
$0
epare proposal
veTek Decision
AL UTILITY ck the tree usin uccessor value dialog box, Tr ility and certain
ns Dialog Box
exponential ut T, where X and as are U = A-B
represent the r determine scal o use exponent change the valu
arded contract
0,000
awarded contract
n Tree
Y AND TR g expected val
es at a decision reePlan will red n equivalent at
tility, the rollba EU are cell re
B*EXP(X/RT)
risk tolerance p ing. If the nam
tial utility, they ues of the nam
Use mechanical method
-$120,000
Try electronic method
-$50,000
Try magnetic method
-$80,000
16.6 Exponenti
REEPLAN lue (probability n node. If you c draw the decisi t each node.
ack formulas a eferences. For t
and CE = LN(
parameter of th mes A, B, and R y are initially d
mes using the In
0.5 Electronic success
$0
0.5 Electronic failure
$0
0.7 Magnetic success
$0
0.3 Magnetic failure
$0
ial Utility and Tre
N y-weighted ave choose to use e ion tree diagram
are U = A–B*E the Minimize o ((A-EU)/B)*RT
he exponential RT don't exist o defined as A=1 nsert > Name >
Use mechanical 1
-$120,000
Use mechanical 1
-$120,000
eePlan 211
erage) at an exponential m with
EXP(X/RT) option with T.
utility on the , B=1, and
> Define
$80,000
$150,000
method $30,000
$120,000
method $0
-$50,000
$0
212 Chapter 16 Decision Trees Using TreePlan
16.7 ACKNOWLEDGEMENT TreePlan was developed by Professor Michael R. Middleton at the University of San Francisco (using the Excel 4 XLM macro programming language) and modified for use at Fuqua (Duke University) by Professor James E. Smith. Mike Middleton rewrote portions using VBA during 2008-2014.