Download - Civil Systems Planning Benefit/Cost Analysis
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Civil Systems PlanningBenefit/Cost Analysis
Scott MatthewsCourses: 12-706 / 19-702/ 73-359Lecture 16
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Admin
Project 1 - avg 85 (high 100)Mid sem grades today - how done?
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Recall: Choosing a Car Example
Car Fuel Eff (mpg) Comfort
IndexMercedes 25 10Chevrolet 28 3Toyota 35 6Volvo 30 9
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“Pricing out”
Book uses $ / unit tradeoffOur example has no $ - but same idea“Pricing out” simply means knowing
your willingness to make tradeoffsAssume you’ve thought hard about the
car tradeoff and would trade 2 units of C for a unit of F (maybe because you’re a student and need to save money)
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With these weights..
U(M) = 0.26*1 + 0.74*0 = 0.26U(V) = 0.26*(6/7) + 0.74*0.5 = 0.593U(T) = 0.26*(3/7) + 0.74*1 = 0.851U(H) = 0.26*(4/7) + 0.74*0.6 = 0.593
Note H isnt really an option - just “checking” that we get same U as for Volvo (as expected)
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MCDM - Swing Weights
Use hypothetical combinations to determine weights
Base option = worst on all attributesOther options - “swings” one of the
attributes from worst to bestDetermine your rank preference, find
weights
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Add 1 attribute to car (cost)
M = $50,000 V = $40,000 T = $20,000 C=$15,000
Swing weight table:Benchmark 25mpg, $50k, 3 Comf
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Stochastic Dominance “Defined”
A is better than B if:Pr(Profit > $z |A) ≥ Pr(Profit > $z |B),
for all possible values of $z.Or (complementarity..)Pr(Profit ≤ $z |A) ≤ Pr(Profit ≤ $z |B),
for all possible values of $z.A FOSD B iff FA(z) ≤ FB(z) for all z
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Stochastic Dominance:Example #1CRP below for 2 strategies shows
“Accept $2 Billion” is dominated by the other.
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Stochastic Dominance (again) Chapter 4 (Risk Profiles) introduced deterministic
and stochastic dominance We looked at discrete, but similar for continuous How do we compare payoff distributions? Two concepts: A is better than B because A provides unambiguously
higher returns than B A is better than B because A is unambiguously less risky
than B If an option Stochastically dominates another, it must
have a higher expected value
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First-Order Stochastic Dominance (FOSD) Case 1: A is better than B because A provides
unambiguously higher returns than B Every expected utility maximizer prefers A to B (prefers more to less) For every x, the probability of getting at least x is higher
under A than under B. Say A “first order stochastic dominates B” if:
Notation: FA(x) is cdf of A, FB(x) is cdf of B. FB(x) ≥ FA(x) for all x, with one strict inequality or .. for any non-decr. U(x), ∫U(x)dFA(x) ≥ ∫U(x)dFB(x) Expected value of A is higher than B
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FOSD
Source: http://www.nes.ru/~agoriaev/IT05notes.pdf
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FOSD Example
Option A Option B
Profit ($M) Prob.
0 ≤ x < 5 0.25 ≤ x < 10 0.310 ≤ x < 15
0.4
15 ≤ x < 20
0.1
Profit ($M) Prob.
0 ≤ x < 5 05 ≤ x < 10 0.110 ≤ x < 15
0.5
15 ≤ x < 20
0.3
20 ≤ x < 25
0.1
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First-Order Stochastic Dominance
00.20.40.60.8
1
0 5 10 15 20 25Profit ($millions)
Cumulative Probability
AB
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Second-Order Stochastic Dominance (SOSD) How to compare 2 lotteries based on risk
Given lotteries/distributions w/ same mean So we’re looking for a rule by which we can say “B
is riskier than A because every risk averse person prefers A to B”
A ‘SOSD’ B if For every non-decreasing (concave) U(x)..
€
U(x)dFA (x)0
x
∫ ≥ U(x)dFB (x)0
x
∫
€
[FB (x) − FA (x)]dx0
x
∫ ≥ 0,∀x
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SOSD Example
Option A Option B
Profit ($M) Prob.
0 ≤ x < 5 0.15 ≤ x < 10 0.310 ≤ x < 15
0.4
15 ≤ x < 20
0.2
Profit ($M) Prob.
0 ≤ x < 5 0.35 ≤ x < 10 0.310 ≤ x < 15
0.2
15 ≤ x < 20
0.1
20 ≤ x < 25
0.1
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Second-Order Stochastic Dominance
00.20.40.60.8
1
0 5 10 15 20 25Profit ($millions)
Cumulative Probability
AB
Area 2
Area 1
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SOSD
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SD and MCDM
As long as criteria are independent (e.g., fun and salary) then Then if one alternative SD another on
each individual attribute, then it will SD the other when weights/attribute scores combined
(e.g., marginal and joint prob distributions)
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Reading pdf/cdf graphs
What information can we see from just looking at a randomly selected pdf or cdf?