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Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ?
Insurance of Natural CatastrophesWhen Should Government Intervene ?
Arthur Charpentier & Benoît le Maux
Université Rennes 1 & École Polytechnique
http ://freakonometrics.blog.free.fr/
Congrès Annuel de la SCSE, Sherbrooke, May 2011.
1
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 1 INTRODUCTION AND MOTIVATION
1 Introduction and motivation
Insurance is “the contribution of the manyto the misfortune of the few”.
The TELEMAQUE working group, 2005.
Insurability requieres independenceCummins & Mahul (JRI, 2004) or C. (GP, 2008)
2
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 1 INTRODUCTION AND MOTIVATION
1.1 The French cat nat mecanism
=⇒ natural catastrophes means no independence
Drought risk frequency, over 30 years, in France.
3
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 1 INTRODUCTION AND MOTIVATION
INSURANCE COMPANY
INSURANCE COMPANY
INSURANCE COMPANY
RE-INSURANCE COMPANYCAISSE CENTRALE DE REASSURANCE
GOVERNMENT
4
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 1 INTRODUCTION AND MOTIVATION
INSURANCE COMPANY
INSURANCE COMPANY
RE-INSURANCE COMPANYCAISSE CENTRALE DE REASSURANCE
GOVERNMENT
INSURANCE COMPANY
5
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 1 INTRODUCTION AND MOTIVATION
INSURANCE COMPANY
INSURANCE COMPANY
RE-INSURANCE COMPANYCAISSE CENTRALE DE REASSURANCE
GOVERNMENT
INSURANCE COMPANY
6
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 2 DEMAND FOR INSURANCE
2 Demand for insurance
An agent purchases insurance if
E[u(ω −X)]︸ ︷︷ ︸no insurance
≤ u(ω − α)︸ ︷︷ ︸insurance
i.e.p · u(ω − l) + [1− p] · u(ω − 0)︸ ︷︷ ︸
no insurance
≤ u(ω − α)︸ ︷︷ ︸insurance
i.e.E[u(ω −X)]︸ ︷︷ ︸
no insurance
≤ E[u(ω − α−l + I)]︸ ︷︷ ︸insurance
Doherty & Schlessinger (1990) considered a model which integrates possiblebankruptcy of the insurance company, but as an exogenous variable. Here, wewant to make ruin endogenous.
7
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 2 DEMAND FOR INSURANCE
Yi =
0 if agent i claims a loss1 if not
Let N = Y1 + · · ·+Xn denote the number of insured claiming a loss, andX = N/n denote the proportions of insured claiming a loss, F (x) = P(X ≤ x).
P(Yi = 1) = p for all i = 1, 2, · · · , n
Assume that agents have identical wealth ω and identical vNM utility functionsu(·).
=⇒ exchangeable risks
Further, insurance company has capital C = n · c, and ask for premium α.
8
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 2 DEMAND FOR INSURANCE
2.1 Private insurance companies with limited liability
Consider n = 5 insurance policies, possible loss $1, 000 with probability 10%.Company has capital C = 1, 000.
Ins. 1 Ins. 1 Ins. 3 Ins. 4 Ins. 5 TotalPremium 100 100 100 100 100 500Loss - 1,000 - 1,000 - 2,000
Case 1 : insurance company with limited liabilityindemnity - 750 - 750 - 1,500loss - -250 - -250 - -500
net -100 -350 -100 -350 -100 -1000
9
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 2 DEMAND FOR INSURANCE
2.2 Possible government intervention
Ins. 1 Ins. 1 Ins. 3 Ins. 4 Ins. 5 TotalPremium 100 100 100 100 100 500Loss - 1,000 - 1,000 - 2,000
Case 2 : possible government interventionTax -100 100 100 100 100 500indemnity - 1,000 - 1,000 - 2,000net -200 -200 -200 -200 -200 -1000
(note that it is a zero-sum game).
10
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 3 A ONE REGION MODEL WITH HOMOGENEOUS AGENTS
3 A one region model with homogeneous agents
Let U(x) = u(ω + x) and U(0) = 0.
3.1 Private insurance companies with limited liability
• the company has a positive profit if N · l ≤ n · α• the company has a negative profit if n · α ≤ N · l ≤ C + n · α• the company is bankrupted if C + n · α ≤ N · l
=⇒ ruin of the insurance company if X ≥ x = c+αl
The indemnity function is
I(x) =
l if X ≤ xc+ α
nif X > x
11
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 3 A ONE REGION MODEL WITH HOMOGENEOUS AGENTS
RuinRuinRuinRuin
––––cncncncn
x α � c
l
α
l
10
Positive profitPositive profitPositive profitPositive profit
[0 ; [0 ; [0 ; [0 ; nnnnα[[[[
Negative profitNegative profitNegative profitNegative profit
]]]]––––cncncncn ;;;; 0[0[0[0[
IIII(X)(X)(X)(X)
Probability of no ruin:
F(x)
Probability of ruin:
1–F(x)
XXXX
Il
c�α
12
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 3 A ONE REGION MODEL WITH HOMOGENEOUS AGENTS
Without ruin, the objective function of the insured is V (α, p, δ, c) defined asU(−α). With possible ruin, it is
E[E(U(−α− loss)|X)]) =∫
E(U(−α− loss)|X = x)f(x)dx
where E(U(−α− loss)|X = x) is equal to
P(claim a loss|X = x) · U(α− loss(x)) + P(no loss|X = x) · U(−α)
i.e.E(U(−α− loss)|X = x) = x · U(−α− l + I(x)) + (1− x) · U(−α)
so thatV =
∫ 1
0[x · U(−α− l + I(x)) + (1− x) · U(−α)]f(x)dx
that can be written
V = U(−α)−∫ 1
0x[U(−α)− U(−α− l + I(x))]f(x)dx
And an agent will purchase insurance if and only if V > p · U(−l).
13
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 3 A ONE REGION MODEL WITH HOMOGENEOUS AGENTS
3.2 Distorted risk perception by the insured
We’ve seen that
V = U(−α)−∫ 1
0x[U(−α)− U(−α− l + I(x))]f(x)dx
since P(Yi = 1|X = x) = x (while P(Yi = 1) = p).
But in the model in the Working Paper (first version), we wrote
V = U(−α)−∫ 1
0p[U(−α)− U(−α− l + I(x))]f(x)dx
i.e. the agent see x through the payoff function, not the occurence probability(which remains exogeneous).
14
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 3 A ONE REGION MODEL WITH HOMOGENEOUS AGENTS
3.3 Government intervention (or mutual fund insurance)
The tax function is
T (x) =
0 if X ≤ xNl − (α+ c)n
n= Xl − α− c if X > x
Then
V =∫ 1
0[x · U(−α− T (x)) + (1− x) · U(−α− T (x))]f(x)dx
i.e.
V =∫ 1
0U(−α+ T (x))f(x)dx = F (x) · U(−α) +
∫ 1
x
U(−α− T (x))f(x)dx
15
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 4 THE COMMON SHOCK MODEL
4 The common shock model
Consider a possible natural castrophe, modeled as an heterogeneous latentvariable Θ, such that given Θ, the Yi’s are independent, and P(Yi = 1|Θ = Catastrophe) = pC
P(Yi = 1|Θ = No Catastrophe) = pN
Let p? = P(Cat). Then the distribution of X is
F (x) = P(N ≤ [nx]) = P(N ≤ k|No Cat)× P(No Cat) + P(N ≤ k|Cat)× P(Cat)
=k∑j=0
(n
j
)[(pN )j(1− pN )n−j(1− p∗) + (pC)j(1− pC)n−jp∗]
16
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 4 THE COMMON SHOCK MODEL
●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●
●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●
●●●●●●●●●●●●●●●●●
●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Share of the population claiming a loss
Cum
ulat
ive
dist
ribut
ion
func
tion
F
pN pCp
1−p*
0.0 0.2 0.4 0.6 0.8 1.0
05
1015
20
Share of the population claiming a loss
Pro
babi
lity
dens
ity fu
nctio
n f
pN pCp
17
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 4 THE COMMON SHOCK MODEL
●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●
●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●
●●●●●●●●●●●●●●●●●
●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Share of the population claiming a loss
Cum
ulat
ive
dist
ribut
ion
func
tion
F
pN pCp
1−p*
0.0 0.2 0.4 0.6 0.8 1.0
05
1015
20
Share of the population claiming a loss
Pro
babi
lity
dens
ity fu
nctio
n f
18
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 4 THE COMMON SHOCK MODEL
●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●
●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●
●●●●●●●●●●●●●●●●●
●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●●
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Share of the population claiming a loss
Cum
ulat
ive
dist
ribut
ion
func
tion
F
pN pCp
1−p*
0.0 0.2 0.4 0.6 0.8 1.0
05
1015
20
Share of the population claiming a loss
Pro
babi
lity
dens
ity fu
nctio
n f
19
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 4 THE COMMON SHOCK MODEL
4.1 Equilibriums in the EU framework
The expected profit of the insurance company is
Π(α, p, δ, c) =∫ x̄
0[nα− xnl] f(x)dx− [1− F (x̄)]cn (1)
Note that a premium less than the pure premium can lead to a positive expectedprofit.
In Rothschild & Stiglitz (QJE, 1976) a positive profit was obtained if and only ifα > p · l. Here companies have limited liabilities.Proposition1If agents are risk adverse, for a given premium , their expected utility is always higherwith government intervention.
Démonstration. Risk adverse agents look for mean preserving spreadlotteries.
20
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 4 THE COMMON SHOCK MODEL
Proposition2From the expected utilities V , we obtain the following comparative static derivatives :
∂V
∂δ< 0 for x̄ > x∗,
∂V
∂p< 0 for x̄ > x∗,
∂V
∂c> 0 for x̄ ∈ [0; 1], ∂V
∂α=?
for x̄ ∈ [0; 1].Proposition3From the equilibrium premium α∗, we obtain the following comparative staticderivatives :
∂α∗
∂δ< 0 for x̄ > x∗,
∂α∗
∂p=? for x̄ > x∗,
∂α∗
∂c> 0 for x̄ ∈ [0; 1],
21
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 4 THE COMMON SHOCK MODEL
0.00 0.05 0.10 0.15 0.20 0.25
−60
−40
−20
0
Premium
Exp
ecte
d ut
ility
pU(−l)= −63.9
●●
●
●● ●pU(−l)= −63.9
Expected profit<0 Expected profit>0
22
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 4 THE COMMON SHOCK MODEL
4.2 Equilibriums in the non-EU framework
Assuming that the agents distort probabilities, they have to compare twointegrals,
V = U(−α)−∫ 1
x
Ak(x)f(x)dx
With government
intervention
x
(1–p)U(–α)+pU(c–l)
U(–α)
U(c–l) X
Expected uExpected uExpected uExpected utilitytilitytilitytility
1
x X
Probability Probability Probability Probability densitydensitydensitydensity functionfunctionfunctionfunction
1 p p
Slightly high correlation Very high correlation
Without government
intervention
High correlation
p
23
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 4 THE COMMON SHOCK MODEL
0.00 0.05 0.10 0.15 0.20 0.25
−60
−40
−20
0
Premium
Exp
ecte
d ut
ility
pU(−l)= −63.9
●●
●
●●●pU(−l)= −63.9
Expected profit<0 Expected profit>0
24
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
5 The 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.
25
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
X1 ∼ F1(x1|p, δ1) = F1(x1), (2)X2 ∼ F2(x2|p, δ2) = F2(x2), (3)X0 ∼ F0(x0|F1, F2, θ) = F0(x0|p, δ1, δ2, θ) = F0(x0), (4)
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− piN/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}.
26
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Share of the population claiming a loss
Cum
ulat
ive
dist
ribut
ion
func
tion
pN1 pC1p
1−p*
− Correlation beween: 0.01
− Region 1: within−correlation: 0.5
− Region 2: within−correlation: 0.5
0.0 0.2 0.4 0.6 0.8 1.0
05
1015
2025
30
Share of the population claiming a loss
Pro
babi
lity
dens
ity fu
nctio
n
27
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Share of the population claiming a loss
Cum
ulat
ive
dist
ribut
ion
func
tion
pN1 pC1p
1−p*
− Correlation beween: 0.1
− Region 1: within−correlation: 0.5
− Region 2: within−correlation: 0.5
0.0 0.2 0.4 0.6 0.8 1.0
05
1015
2025
30
Share of the population claiming a loss
Pro
babi
lity
dens
ity fu
nctio
n
28
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Share of the population claiming a loss
Cum
ulat
ive
dist
ribut
ion
func
tion
pN1 pC1p
1−p*
− Correlation beween: 0.01
− Region 1: within−correlation: 0.5
− Region 2: within−correlation: 0.7
0.0 0.2 0.4 0.6 0.8 1.0
05
1015
2025
30
Share of the population claiming a loss
Pro
babi
lity
dens
ity fu
nctio
n
29
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
0.0 0.2 0.4 0.6 0.8 1.0
0.0
0.2
0.4
0.6
0.8
1.0
Share of the population claiming a loss
Cum
ulat
ive
dist
ribut
ion
func
tion
pN1 pC1p
1−p*
− Correlation beween: 0.01
− Region 1: within−correlation: 0.5
− Region 2: within−correlation: 0.3
0.0 0.2 0.4 0.6 0.8 1.0
05
1015
2025
30
Share of the population claiming a loss
Pro
babi
lity
dens
ity fu
nctio
n
30
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
Proposition4When both regions decide to purchase insurance, the two-region models of naturalcatastrophe insurance lead to the following comparative static derivatives :
∂Vi,0∂αj
> 0, ∂α∗∗i
∂α∗∗j
> 0, for i = 1, 2 and j 6= i.
31
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
Study of the two region modelThe 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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Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
REGION 1
BUYS
INSURANCE
REGION 1
BUYS NO
INSURANCE
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miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
REGION 1
BUYS
INSURANCE
REGION 1
BUYS NO
INSURANCE
32
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
Study of the two region modelThe 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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Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
REGION 2
BUYS NO
INSURANCE
REGION 2
BUYS
INSURANCE
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Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
REGION 2
BUYS NO
INSURANCE
REGION 2
BUYS
INSURANCE
33
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
Definition1In a Nash equilibrium which each player is assumed to know the equilibrium strategiesof the other players, and no player has anything to gain by changing only his or her ownstrategy unilaterally.
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Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
REGION 1
BUYS
INSURANCE
REGION 1
BUYS NO
INSURANCE
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●●
●●
●●
●●
●●
●●
●
Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
REGION 1
BUYS
INSURANCE
REGION 1
BUYS NO
INSURANCE
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
REGION 2
BUYS NO
INSURANCE
REGION 2
BUYS
INSURANCE
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
REGION 2
BUYS NO
INSURANCE
REGION 2
BUYS
INSURANCE
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
34
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
Definition2In a Nash equilibrium which each player is assumed to know the equilibrium strategiesof the other players, and no player has anything to gain by changing only his or her ownstrategy unilaterally.
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: insured
Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: non−insured
Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: insured
Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: non−insured
Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
Premium in Region 1
Pre
miu
m in
Reg
ion
2
0 10 20 30 40 50
010
2030
4050
35
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
Possible Nash equilibriums
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
0 10 20 30 40 50
010
2030
4050
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: insured, 2: non−insured
Premium in Region 1
Prem
ium in
Reg
ion 2
0 10 20 30 40 50
010
2030
4050
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
1: non−insured, 2: insured
Premium in Region 1
Prem
ium in
Reg
ion 2
0 10 20 30 40 50
010
2030
4050
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●●
●
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)
36
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
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)
37
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
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
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
●
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●
●
●
●
●
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●
●
●
●
●
●
●
●
●
●
●
●
−10 0 10 20 30 40
−10
010
2030
40
(−10:40)
(−10
:40)
38
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
When the risks between two regions are not sufficiently independent, the poolingof the risks can lead to a Pareto improvement only if the regions have identicalwithin-correlations, ceteris paribus. If the within-correlations are not equal, thenthe less correlated region needs the premium to decrease to accept the pooling ofthe risks.
39
Arthur CHARPENTIER, Insurance of natural catastrophes: when should governments intervene ? 5 THE TWO REGION MODEL
�� α�
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