influence diag and decision trees - george mason universitymason.gmu.edu/~rganesan/influence diag...
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Decision & Risk Analysis
Influence Diagrams, Decision
Trees
NOTE: Some materials for this presentation courtesy of Dr. Dan Maxwell
Reference: Clemen & Reilly. Making Hard Decisions, 2nd ed. Chapter 3. Duxbury, 2001
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Decision & Risk Analysis
The Elements of a Decision
• Objectives and means
• Alternatives to choose between
• Uncertainty in Events and Outcomes
• Consequences of the Decision
How do we structure the problem?
Common ways of structuring the decision problem:
• Influence Diagrams
• Decision Trees
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Decision & Risk Analysis
Influence Diagrams
Chance
DecisionValue
Chance
(Outcome)
Deterministic
Chance
(outcome)
Information
Arc
Probabilistic
Relevance
Influence
Functional
Relevance
Three Levels of
Specification
Courtesy of Dr. Dan Maxwell
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Decision & Risk Analysis
A Simple Influence Diagram
Figure 3.5
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Decision & Risk Analysis
Showing Influence with Arrows
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Decision & Risk Analysis
Objectives Hierarchy into
Influence Diagram
Maximize Overall Satisfaction
Invest in Computer Industry Return on Investment
Invest?
Return on
Investment
Computer
Industry Growth
Venture Succeeds
or Fails
Overall
SatisfactionFigure 3.6
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Decision & Risk Analysis
Multiple Objectives
Figure 3.7
Note: The Oval
Shape can be Used
as well as the
Diamond Shape for
the Final Satisfaction
Node
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Decision & Risk Analysis
Basic Diagram for Investment
Savings Success 2200Flop 2200
Business Success 5000Flop 0
Wild Success
Flop
SavingsBusiness
Figure 3.9
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Decision & Risk Analysis
An Influence Diagram for Evacuation
FIGURE 3.11
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Decision & Risk Analysis
Sequential Decision Problems
FIGURE 3.13
Note: Payoff = Cash Flow;
Total Payoff = Net Present Value
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Decision & Risk Analysis
A Simple Influence Diagram for
New Product
FIGURE 3.14
NOTE alternative
method of
representing payoff
(consequence) node
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Decision & Risk Analysis
New Product - Additional Detail
FIGURE 3.15
Profit
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Decision & Risk Analysis
Deterministic Nodes
ProfitIntroduce
Product?
Price?
Units
Sold
Fixed
CostUnit
Variable
Cost
Revenue Cost
Figure 3.16
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Decision & Risk Analysis
Another Representation of
Deterministic Nodes
FIGURE 3.16
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Decision & Risk Analysis
Starting an Influence Diagram
FIGURE 3.18
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Decision & Risk Analysis
Intermediate Step
FIGURE 3.19
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Decision & Risk Analysis
A Completed Influence Diagram
FIGURE 3.20
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Decision & Risk Analysis
Decision Tree Representation
FIGURE 3.21
Influence
Diagram
Representation
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Decision & Risk Analysis
Decision Trees – Dealing with Uncertainty
• Probabilities replace the weights
– Account for uncertainty
– Used to evaluate expected values
• Example - Venture Capital Problem
Decision
represented
by box
Uncertain outcome
represented by circleR
L < 0
success
failure
p
1 - pinves
t
Do not
invest
savingsr
Large return
Loss
Small return
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Decision & Risk Analysis
Decision Trees (continued)• Expected return on investment:
– If investment is made E(I) = pR + (1 - p)L
– If investment not made E(N) = r
• Decision:
– Invest if pR + (1 - p)L > r
– Don’t invest if r > pR + (1 - p)L
What would you do if r = pR + (1 - p)L?
• Decision Trees evaluated left to right
decision must be made before uncertain
event takes place
decision is conditional on the known
outcome of the uncertain event
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Decision & Risk Analysis
ExampleDo I take my umbrella or not?
– If I don’t and it is sunny, that is best - value 1.00
– If I do I won’t get wet but it’s inconvenient
- value 0.80
– If I don’t and it rains I ruin my suit - value 0.00
– Probability of sunshine is pPayoff
sunshine
sunshine
rain
rain
p
p
1 - p
1 - p
0.00
1.00
0.80
0.80
Payoff Calculation:
– Take umbrella
0.8p + 0.8(1-p) = 0.8
– Don’t take umbrella
1.0p + 0(1-p) = p
Therefore:
Take umbrella if
p < 0.8
Take
Umbrella
Don’t take
Umbrella
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Decision & Risk Analysis
Basic Decision Tree
FIGURE 3.25
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Decision & Risk Analysis
Sequential Decisions
Evacuate NowSafety, High Cost
Wait
for Forecast
Forecast: “Will
Hit Miami
Forecast: “Will
Miss Miami
Stay
Hurricane
Hits Miami
Hurricane
Misses Miami
Danger, Low Cost
Safety, Low Cost
Evacuate Safety, High Cost
Hurricane
Hits Miami
Hurricane
Misses Miami
Danger, Low Cost
Safety, Low Cost
Evacuate Safety, High Cost
Stay
Figure 3.29
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Decision & Risk Analysis
Sequential Decision Tree
FIGURE 3.30
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Decision & Risk Analysis
Influence Diagram or Decision Tree
Influence Diagram Decision Trees
1. Gives basic information 1.Gives detailed info
2. Less messy 2.More messy due to
greater details
3. Graphically more appealing 3.Not so appealing
when presented to upper management
Must be viewed as complementary techniques. One strategy is to
start with influence diagram and fill in the details to develop a
decision tree.