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Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Couverture du risque de catastrophenaturelle dans un jeu non cooperatif
Arthur Charpentier∗ & Benoıt Le Maux
http ://blogperso.univ-rennes1.fr/arthur.charpentier/
∗ CREM-Universite Rennes 1 & Ecole Polytechnique
Journees AST&Risk, Grenoble Aout 2009
1
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Decision theory with uncertainty, classical models
Consider an agent with utility function u(·), facing possible loss l > 0 withprobability p.
• without insurance, E(u(X)) = p · u(−l) + (1− p) · u(0) = p · u(−l)• without insurance, E(u(X)) = u(−α)
where α denotes the insurance premium, with convention u(0) = 0. Thus, let
α? = −u−1 (pu(−l))
• if α < α? the agent buys insurance• if α > α? the agent does not buys insurance
2
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Decision theory with uncertainty, with possible ruin
Assume that ruin is possible. Let N denote the number of insured claiming, thenthere is ruin if
C + nα < Nl orN
n= X >
C/n+ α
l=c+ α
l= x
In case of ruin two cases can be considered• ‘insurance company with limited liability’ : the total amount of asset is divided
among the insured claiming losses (prorata capita)• ‘mutual insurance company’ : there is no ruin since the insurance company will
ask for an additional premium to all the insured to pay that difference
3
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
insurance company Ltd. versus mutual insurance
Ins. 1 Ins. 1 Ins. 3 Ins. 4 Ins. 5 Total
Premium 100 100 100 200 200 700
Loss - 400 - 600 - 1000
Case 1 : insurance company with limited liability
payment - 320 - 480 - 800
Case 2 : mutual insurance company
payment 400 600 1000
-29 -29 -29 -57 -57 -200
final payment -29 371 -29 543 -57 800
4
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Possible ruin, insurance company with limited liability
• if X = N/n ∈ [0, α/l] : positive profit, I(x) = l
• if X = N/n ∈ [α/l, x] : negative profit, I(x) = l
• if X = N/n ∈ [x, 1] : ruin, I(x) ∈ [0, l]
where x = (α+ c)/l.
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
5
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Possible ruin, insurance company with limited liability
With insurance, the expected value for an agent with utility function u(·) was (inthe classical model), with random loss L
E(u(L)) = pu(−α− l + l) + (1− p)u(−α) = u(−α)
but if ruin is possible, it becomes
E(u(L)) = pE((u(−α− l + I(X))) + (1− p)u(−α)
Hence, if F and f are cdf and the pdf of X,
E(u(L)) = p ·F (x) ·U(−α) + p ·F (x) ·∫ 1
x
U(−α− l+ I(x))f(x)dx+ (1− p)u(−α)
6
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Possible ruin, insurance company with limited liability
Expected utility of a representative agent without ruin, or with possible ruin,
Premium
0.0 0.5 1.0 1.5 2.0
=⇒ a low premium is not (necessarily) interesting (high risk of bankrupt).
7
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A model with dependence among risks
Consider a common chock model, i.e. Θ is the indicator of occurrence of acatastrophe. Given Θ, the Zi are independent,• if Θ = 0, Zi ∼ B(pN ), i.e. N = Z1 + · · ·+ Zn ∼ B(n, pN ), no catastrophe• if Θ = 1, Zi ∼ B(pC), i.e. N = Z1 + · · ·+ Zn ∼ B(n, pC), catastrophe
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
8
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A model with dependence among risks
P(N ≤ k) =k∑
j=0
(j
n
)[pj
C(1− pC)n−jp? + pjN (1− pN )n−j(1− p?)
]where p? = P(Θ = 1), pC = P(Zi = 1|Θ = 1) and pN = P(Zi = 1|Θ = 0).
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
9
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Getting a better understanding of the model
Let p = P(Zi = 1) (individual loss probability). Consider an increase of p
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Proportion of insured claiming
Pro
babi
lity
(cum
ulat
ed)
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
p1 ≤ p2 =⇒ Θ1 �1 Θ2 =⇒ F1 �1 F2
10
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Getting a better understanding of the model
Let δ = 1− pN/pC , so that δ can be seen as a correlation within the region.
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Proportion of insured claiming
Pro
babi
lity
(cum
ulat
ed)
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
δ1 ≤ δ2 =⇒ Θ1 �2 Θ2 =⇒ F1 �2 F2
11
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Getting a better understanding of the model
The impact of the number of insurerd n
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Proportion of insured claiming
Pro
babi
lity
(cum
ulat
ed)
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
12
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Impact of parameters on ruin probability
• increase of p, claim occurrence probability : increase of ruin probability for allx ∈ [0, 1]
• increase of δ, within correlation : there exists x0 ∈ (0, 1) such that◦ increase of ruin probability for all x ∈ [x0, 1]◦ decrease of ruin probability for all x ∈ [0, x0]
• increase of n, number of insured : there exists x0 ∈ (0, 1) such that◦ decrease of ruin probability for all x ∈ [pC , 1]◦ increase of ruin probability for all x ∈ [x0, pC ]◦ decrease of ruin probability for all x ∈ [pN , x0]◦ increase of ruin probability for all x ∈ [0, pN ]
• increase of c, economic capital : decrease of ruin probability for all x ∈ [0, 1]• increase of α, individual premium : decrease of ruin probability for all x ∈ [0, 1]
13
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Impact of parameters on utility functions
... but the impact on utility is more complex, for instance, the impact of δ on theutility is the following
Correlation
0.0 0.2 0.4 0.6 0.8 1.0
14
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A two region model
Consider here a two-region chock model such that• Θ = (0, 0), no catastrophe in the two regions,• Θ = (1, 0), catastrophe in region 1 but not in region 2,• Θ = (0, 1), catastrophe in region 2 but not in region 1,• Θ = (1, 1), catastrophe in the two regions.Let N1 and N2 denote the number of claims in the two regions, respectively, andset N0 = N1 +N2.
15
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A two region model Θ = (1, 1)
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
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proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
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proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
16
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A two region model Θ = (1, 0)
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
17
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A two region model Θ = (0, 1)
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
18
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A two region model Θ = (0, 0)
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
proportion claiming
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
●
19
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
On correlations in this two region model
Note that there are two kinds of correlation in this model,• a within region correlation, with coefficients δ1 and δ2
• a between region correlation, with coefficient δ0Here, δi = 1− pi
N/piC , where i = 1, 2 (Regions), while δ0 ∈ [0, 1] is such that
P(Θ = (1, 1)) = δ0 ×min{P(Θ = (1, ·)),P(Θ = (·, 1))} = δ0 ×min{p?1, p
?2}.
20
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A noncooperative game : who buys insurance ?
In that case, 4 cases should be considered, depending on the region profiles• state s = (I, I), agents buy insurance in the two regions• state s = (I,N), only agents in region 1 buy insurance• state s = (N, I), only agents in region 2 buy insurance• state s = (N,N), no one buys insuranceHence, here everything should be visualized in the the plan (α1, α2). In eachstate s, a representative agent in Region i maximumizes
Vi,s = pi ·Fs(xs) ·U(−αi)+p ·F s(xs) ·∫ 1
x
U(−αi− l+I(x))fs(x)dx+(1−pi)u(−αi)
21
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A noncooperative game : who buys insurance ?
Hence, agents take decisions given the following payoff matrix for a given set ofpremiums (α1, α2),
Region 2
Insure Don’t
Region 1 Insure V1,(I,I), V2,(I,I) V1,(I,N), p2U(−l)
Don’t p1U(−l), V2,(N,I) p1U(−l), p2U(−l)
Note that agents in the two regions can have different risk aversions (or riskperception).
22
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Study of the two region model
The following graphs show the decision in Region 1, given that Region 2 buyinsurance (on the left) or not (on the right).
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REGION 1
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REGION 1
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BUYS NO
INSURANCE
23
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Study of the two region model
The following graphs show the decision in Region 2, given that Region 1 buyinsurance (on the left) or not (on the right).
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REGION 2
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INSURANCE
REGION 2
BUYS
INSURANCE
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REGION 2
BUYS
INSURANCE
24
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Nash equilibrium for a two region model
Definition 1. In a Nash equilibrium which each player is assumed to know theequilibrium strategies of the other players, and no player has anything to gain bychanging only his or her own strategy unilaterally.
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25
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Nash equilibrium for a two region model
Definition 2. In a Nash equilibrium which each player is assumed to know theequilibrium strategies of the other players, and no player has anything to gain bychanging only his or her own strategy unilaterally.
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26
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Possible Nash equilibriums
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1: non−insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
0 10 20 30 40 50
010
2030
4050
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
Premium in Region 1
Prem
ium in
Reg
ion 2
0 10 20 30 40 50
010
2030
4050
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
−10 0 10 20 30 40
−10
010
2030
40
(−10:40)
(−10
:40)
27
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Possible Nash equilibriums
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
−10 0 10 20 30 40
−10
010
2030
40
(−10:40)
(−10
:40)
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
−10 0 10 20 30 40
−10
010
2030
40
(−10:40)
(−10
:40)
28
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Possible Nash equilibriums
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
−10 0 10 20 30 40
−10
010
2030
40
(−10:40)
(−10
:40)
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
−10 0 10 20 30 40
−10
010
2030
40
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
−10 0 10 20 30 40
−10
010
2030
40
(−10:40)
(−10
:40)
29
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Sensilibity to parameters
Impact of catastrophe probability (in region 2), while individual claim occurrenceprobability remains unchanged.
increase of catastrophe probability p?2 decrease of catastrophe probability p?
2
30
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Sensilibity to parameters
Impact of correlation between the two regions, and impact of the economiccapital of the insurance company.
increase of between (region) correlation δ0 increase of economic capital c
31
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Sensilibity to parameters
Impact when the populations are different in the two regions,
increase of number of unhabitants n1 increase of number of unhabitants n2
32
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
Sensilibity to parameters
increase of within correlations δ1 and δ2 increase of within correlation δ1
33
Arthur CHARPENTIER - Couverture du risque de catastrophe naturelle dans un jeu non cooperatif
A short word about Pareto optimality
Definition 3. An allocation is defined as Pareto optimal when no further Paretoimprovements can be made, i.e. a change from one allocation to another that canmake at least one individual better off without making any other individual worseoff.
34