copula and multivariate dependencies for risk models

48
Copula and multivariate dependencies Eric Marsden <[email protected]>

Upload: eric-marsden

Post on 17-Jul-2015

326 views

Category:

Engineering


9 download

TRANSCRIPT

Page 1: Copula and multivariate dependencies for risk models

Copula and multivariate dependencies

Eric Marsden

<[email protected]>

Page 2: Copula and multivariate dependencies for risk models

Warmup. Before reading this material, wesuggest you consult the following associatedslides:

▷ Slides on Modelling correlations withPython

▷ Slides on Estimating Value at Risk

Available from risk-engineering.org &slideshare.net

2 / 41

Page 3: Copula and multivariate dependencies for risk models

Dependencies and risk: stock portfolios

stock A

sto

ck B

both stocksgain strongly

both stockslose strongly

“ordinary” days

both stocksgain

both stockslose

asymmetric days:one up, one down

asymmetric days:one up, one down

3 / 41

Page 4: Copula and multivariate dependencies for risk models

Dependencies and risk: life insurance

▷ Correlation of deaths for life insurance companies• marginal distributions: probabilities of time until death for each spouse

• joint distribution shows the probability of spouses dying in close succession

▷ Aim (actuarial studies): estimate the conditional probability when onespouse dies, that the succeeding spouse will die shortly afterwards

▷ Common risk factors:• common disaster (fatal accidents involving both spouses)

• common lifestyle

• “broken-heart syndrome”

4 / 41

Page 5: Copula and multivariate dependencies for risk models

Dependencies and risk: bank loans

borrower k

borr

ower

j

both j & k pay

both j & kdefault

k pays, j defaults

j pay

s,

k de

faul

ts

▷ Correlation of default: what is the likelihood that if onecompany defaults, another will default soon after?• r = 0: default events are independent

• perfect positive correlation (r=1): if one company defaults,the other will automatically do the same

• perfect negative correlation: if one company defaults, theother will certainly not

Example of correlated defaults

A bank lends money to two companies: a dairy farm and adairy. The farm has a 10% chance of going bust and the dairy a5% chance. But if the farm does go under, the chances that thedairy will follow will quickly rise above 5% if the farm was itsmain milk supplier.

P o o r e s t i ma t i o n o f t h

e s e c o r r e l at i o n s

l e d t o f a i l ur e o f L T C M

h e d g e f u nd

( U S A , 1 9 9 8)

5 / 41

Page 6: Copula and multivariate dependencies for risk models

Dependencies and risk: testing in semiconductor manufacturing

Datasheet specification, uTest specification, t

fails test

passes test

bad in usegood in use

yield loss: fraction rejected bytest, regardless of use

overkill: rejected by test butgood in use

End Use Defect Level: bad in use as fraction of passes test

P e r f o r m a nc e d u r i n g

t e s t i n g i s

c o r r e l a t e dw i t h ( b u t

n o t e x a c t l y

e q u i v a l e n tt o ) p e r f o r

m a n c e i n th e

f i e l d

Source: Copula Methods in Manufacturing Test: A DRAM Case Study, C. Glenn Shirley & W. Robert Daasch

6 / 41

Page 7: Copula and multivariate dependencies for risk models

Dependencies and risk: other applications

Modelling dependencies is an important and widespread issue in risk analysis:

▷ Civil engineering: reliability analysis of highway bridges

▷ Insurance industry: estimating exposure to systemic risks• a hurricane causes deaths, property damage, vehicle damage, business

interruption…

▷ Medicine: failure of paired organs

▷ Note: often the dependency is more complicated than a simple linearcorrelation…

7 / 41

Page 8: Copula and multivariate dependencies for risk models

Copula

▷ Latin word that means “to fasten or fit”

▷ A bridge between marginal distributions and a joint distribution• dependency between stocks (e.g. CAC40 & DAX)

• dependency between defaults on loans

• dependency between annual peak of a river and volume (hydrology)

▷ Widely used in quantitative finance & insurance

▷ Let’s look at plots of a few 2D copula functions to try to visualize theirimpact

8 / 41

Page 9: Copula and multivariate dependencies for risk models

Same copula, different marginals

9 / 41

Page 10: Copula and multivariate dependencies for risk models

Another copula

10 / 41

Page 11: Copula and multivariate dependencies for risk models

Copula representing perfect correlation

11 / 41

Page 12: Copula and multivariate dependencies for risk models

Copula representing perfect negative correlation

12 / 41

Page 13: Copula and multivariate dependencies for risk models

Copula representing independence

13 / 41

Page 14: Copula and multivariate dependencies for risk models

Copula: definitions

▷ Copula functions are a tool to separate the specification of marginaldistributions and the dependence structure• unlike most multivariate statistics, allow combination of different marginals

▷ Say two risks A and B have joint probability H (X , Y ) and marginalprobabilities FX and FY

• H (X , Y ) = C(FX , FY )

• C is a copula function

▷ Characteristics of a copula:• C(1, 1) = 1

• C(x , 0) = 0

• C(0, y) = 0

• C(x , 1) = x

• C(1, y) = y

14 / 41

Page 15: Copula and multivariate dependencies for risk models

Gaussian copula, dimension 2, rho=0.8

1

2

2

3

3

4

4

5

6

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

PDF

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

CDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

dCopula

02

46

810

PDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

pCopula

0.00.2

0.40.6

0.81.0

CDF

15 / 41

Page 16: Copula and multivariate dependencies for risk models

Gaussian copula, dimension 2, rho=-0.9

2

4

4

6

6

8

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

PDF

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

CDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

dCopula

0

5

10

15

PDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

pCopula

0.00.2

0.40.6

0.81.0

CDF

16 / 41

Page 17: Copula and multivariate dependencies for risk models

Gaussian copula, dimension 2, rho=0

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

1

1 1

1

1

1

1

1

1

1

1

1 1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

PDF

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

CDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

dCopula

0.00.2

0.40.6

0.81.0

PDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

pCopula

0.00.2

0.40.6

0.81.0

CDF

17 / 41

Page 18: Copula and multivariate dependencies for risk models

Gaussian copula, dimension 3

18 / 41

Page 19: Copula and multivariate dependencies for risk models

Student t copula, dimension 2, rho=0.8

2

2

4

4

6 8

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

PDF

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

CDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

dCopula

0

5

10

15

PDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

pCopula

0.00.2

0.40.6

0.81.0

CDF

19 / 41

Page 20: Copula and multivariate dependencies for risk models

Gumbel copula, dimension 2, rho=0.8

5

5

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

PDF

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

CDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

dCopula

0

10

20

30

PDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

pCopula

0.00.2

0.40.6

0.81.0

CDF

20 / 41

Page 21: Copula and multivariate dependencies for risk models

Clayton copula, dimension 2, rho=0.8

2

2

4 6

8

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

PDF

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

CDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

dCopula

05

1015

2025

PDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

pCopula

0.00.2

0.40.6

0.81.0

CDF

21 / 41

Page 22: Copula and multivariate dependencies for risk models

Independence copula, C(u, v) = u × v

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

PDF

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

CDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

dCopula

0.00.2

0.40.6

0.81.0

PDF

x

0.00.2

0.40.6

0.81.0

y

0.0

0.2

0.4

0.60.8

1.0

pCopula

0.00.2

0.40.6

0.81.0

CDF

22 / 41

Page 23: Copula and multivariate dependencies for risk models

Copula representing perfect positive dependence

C(u, v) = min(u, v)

0.0

0.2

0.4

0.6

0.8 0.2

0.4

0.6

0.8

1.00.0

0.2

0.4

0.6

0.8

1.0

Upper Fréchet-Hoeffding bound copula

23 / 41

Page 24: Copula and multivariate dependencies for risk models

Copula representing perfect negative dependence

C(u, v) = max(u + v − 1, 0)

0.0

0.2

0.4

0.6

0.8 0.2

0.4

0.6

0.8

1.00.0

0.2

0.4

0.6

0.8

1.0

Lower Fréchet-Hoeffding bound copula

24 / 41

Page 25: Copula and multivariate dependencies for risk models

Tail dependence

▷ Risk management is concerned with the tail of the distribution of losses

▷ Large losses in a portfolio are often caused by simultaneous large moves in severalcomponents

▷ One interesting aspect of any copula is the probability it gives to simultaneousextremes in several dimensions

▷ The lower tail dependence of Xi and Xj is defined as

𝜆l = limu→0

Pr[Xi ≤ F −1i (u)|Xj ≤ F −1

j (u)]

▷ Only depends on the copula, and is limu→01

uCi,j (u, u)

▷ Tail dependence is symmetric• tail dependence of Xi and Xj is the same as that of Xj and Xi

▷ Upper tail dependence 𝜆u is defined similarly25 / 41

Page 26: Copula and multivariate dependencies for risk models

Mathematical recap: joint probability distribution

▷ Joint probability distributions are defined in the form below:

f (x , y) = Pr(X = x , Y = y)

representing the probability that events x and y occur at thesame time

▷ The Cumulative Distribution Function (cdf) for a jointprobability distribution is given by:

FXY (x , y) = Pr(X ≤ x , Y ≤ y)

▷ Note: examples here are bivariate, but principles are valid formultivariate distributions

26 / 41

Page 27: Copula and multivariate dependencies for risk models

Joint distribution — discrete case

b1 b2 b3 … bk

a1 p1,1 p1,2 p1,3 … p1,k

a2 p2,1 p2,2 p2,3 … p2,k

… … … … … …

… … … … … …

am pm,1 pm,2 pm,3 … pm,k

Pr(A = ai and B = aj ) = pi,j

27 / 41

Page 28: Copula and multivariate dependencies for risk models

Joint distribution — continuous case

▷ fXY ∶ Rn → R

▷ fXY ≥ 0 ∀v ∈ Rn

▷ ∫∞−∞

∫∞−∞ fXY (x , y) = 1

▷ Pr(v ∈ B) = ∬BfXY

▷ Pr(X ≤ x ) = FX (x ) = ∫x−∞ FX (z)dz

▷ Pr(Y ≤ y) = FY (y) = ∫y−∞ FY (z)dz

▷ Pr(X ≤ x , Y ≤ y) = FXY (x , y) =∫x−∞

∫y−∞ fXY (w , z)dw  dz

−1 −0.5 0 0.5 1 1.5 2 2.5 3 3.5 4

0

2

4

0

0.1

0.2

0.3

0.4

0.5𝑃(𝑥1)

𝑃(𝑥2)

𝑥1

𝑥2

𝑃Bivariate gaussian distribution

28 / 41

Page 29: Copula and multivariate dependencies for risk models

Marginal distributions — discrete case

b1 b2 b3 … bk

a1 p1,1 p1,2 p1,3 … p1,k

a2 p2,1 p2,2 p2,3 … p2,k

… … … … … …

… … … … … …

am pm,1 pm,2 pm,3 … pm,k

pX (x ) = Pr(X = x ) = ∑y

p(x , y)

pY (y) = Pr(Y = y) = ∑x

p(x , y)

29 / 41

Page 30: Copula and multivariate dependencies for risk models

Marginal distributions — discrete case

b1 b2 b3 … bk

a1 p1,1 p1,2 p1,3 … p1,k

a2 p2,1 p2,2 p2,3 … p2,k

… … … … … …

… … … … … …

am pm,1 pm,2 pm,3 … pm,k

pX (x ) = Pr(X = x ) = ∑y

p(x , y)

pY (y) = Pr(Y = y) = ∑x

p(x , y)

29 / 41

Page 31: Copula and multivariate dependencies for risk models

Marginal distributions — continuous case

fX (x ) = ∫∞

−∞f (x , y)dy

fY (y) = ∫∞

−∞f (x , y)dx

30 / 41

Page 32: Copula and multivariate dependencies for risk models

Sklar’s theorem

For every joint probability distribution FXY there is a copula C such that:

FXY (x , y) = C ( FX (x ), FY (y))

copula function

marginaldistribution of X

marginaldistribution of Y

If FXY is continuous then C is unique.

31 / 41

Page 33: Copula and multivariate dependencies for risk models

Copula: summary

▷ Copula captures the dependency between the random variables

▷ Marginals capture individual distributions

▷ Sklar’s theorem “glues” them together

▷ “Shape” and degree of joint tail dependence is a copula property• are independent of the marginals

32 / 41

Page 34: Copula and multivariate dependencies for risk models

Understanding the copula function

X

Y

space of our “realvariables”

x

y

0

1t

FXY (x , y) = t

joint distribution function

FXY (x , y) = t is the probability thatX < x and Y < y

FX (x)

FY (y)(x, y)

We can use the marginal CDFs tomap from (x , y) to a point (u, v)on the unit square.

1

0 0 1

(u, v)F −1X (·)

F −1Y (·)

(F −1X (u), F −1

Y (v))

We can use the marginal inverseCDFs to map from (u, v) to(F −1

X (u), F −1Y (v)).

(F −1X (u), F −1

Y (v))

0

1t = FXY (F −1

X (u), F −1Y (v))

FXY (·, ·)

joint distribution function

Then map from (F −1X (u), F −1

Y (v)) to[0, 1] using the joint distributionfunction.

0

1t = C(u, v)

1

0 0 1

(u, v)

FXY

(F −1X , F −1

Y ) C

C(u, v) = FXY (F −1X (u), F −1

Y (v))

The copula function lets us mapdirectly from the unit square tothe joint distribution.

It lets us express the jointprobability as a function of themarginal distributions.

FXY (x , y) = C (FX (x), FY (y))

33 / 41

Page 35: Copula and multivariate dependencies for risk models

Understanding the copula function

X

Y

x

y

0

1t

FXY (x , y) = t

joint distribution function

FXY (x , y) = t is the probability thatX < x and Y < y

FX (x)

FY (y)(x, y)

We can use the marginal CDFs tomap from (x , y) to a point (u, v)on the unit square.

1

0 0 1

(u, v)F −1X (·)

F −1Y (·)

(F −1X (u), F −1

Y (v))

We can use the marginal inverseCDFs to map from (u, v) to(F −1

X (u), F −1Y (v)).

(F −1X (u), F −1

Y (v))

0

1t = FXY (F −1

X (u), F −1Y (v))

FXY (·, ·)

joint distribution function

Then map from (F −1X (u), F −1

Y (v)) to[0, 1] using the joint distributionfunction.

0

1t = C(u, v)

1

0 0 1

(u, v)

FXY

(F −1X , F −1

Y ) C

C(u, v) = FXY (F −1X (u), F −1

Y (v))

The copula function lets us mapdirectly from the unit square tothe joint distribution.

It lets us express the jointprobability as a function of themarginal distributions.

FXY (x , y) = C (FX (x), FY (y))

33 / 41

Page 36: Copula and multivariate dependencies for risk models

Understanding the copula function

X

Y

x

y

0

1t

FXY (x , y) = t

joint distribution function

FXY (x , y) = t is the probability thatX < x and Y < y

FX (x)

FY (y)(x, y)

We can use the marginal CDFs tomap from (x , y) to a point (u, v)on the unit square.

1

0 0 1

(u, v)

F −1X (·)

F −1Y (·)

(F −1X (u), F −1

Y (v))

We can use the marginal inverseCDFs to map from (u, v) to(F −1

X (u), F −1Y (v)).

(F −1X (u), F −1

Y (v))

0

1t = FXY (F −1

X (u), F −1Y (v))

FXY (·, ·)

joint distribution function

Then map from (F −1X (u), F −1

Y (v)) to[0, 1] using the joint distributionfunction.

0

1t = C(u, v)

1

0 0 1

(u, v)

FXY

(F −1X , F −1

Y ) C

C(u, v) = FXY (F −1X (u), F −1

Y (v))

The copula function lets us mapdirectly from the unit square tothe joint distribution.

It lets us express the jointprobability as a function of themarginal distributions.

FXY (x , y) = C (FX (x), FY (y))

33 / 41

Page 37: Copula and multivariate dependencies for risk models

Understanding the copula function

X

Y

x

y

0

1t

FXY (x , y) = t

joint distribution function

FXY (x , y) = t is the probability thatX < x and Y < y

FX (x)

FY (y)(x, y)

We can use the marginal CDFs tomap from (x , y) to a point (u, v)on the unit square.

1

0 0 1

(u, v)F −1X (·)

F −1Y (·)

(F −1X (u), F −1

Y (v))

We can use the marginal inverseCDFs to map from (u, v) to(F −1

X (u), F −1Y (v)).

(F −1X (u), F −1

Y (v))

0

1t = FXY (F −1

X (u), F −1Y (v))

FXY (·, ·)

joint distribution function

Then map from (F −1X (u), F −1

Y (v)) to[0, 1] using the joint distributionfunction.

0

1t = C(u, v)

1

0 0 1

(u, v)

FXY

(F −1X , F −1

Y ) C

C(u, v) = FXY (F −1X (u), F −1

Y (v))

The copula function lets us mapdirectly from the unit square tothe joint distribution.

It lets us express the jointprobability as a function of themarginal distributions.

FXY (x , y) = C (FX (x), FY (y))

33 / 41

Page 38: Copula and multivariate dependencies for risk models

Understanding the copula function

X

Y

x

y

0

1t

FXY (x , y) = t

joint distribution function

FXY (x , y) = t is the probability thatX < x and Y < y

FX (x)

FY (y)(x, y)

We can use the marginal CDFs tomap from (x , y) to a point (u, v)on the unit square.

1

0 0 1

(u, v)F −1X (·)

F −1Y (·)

(F −1X (u), F −1

Y (v))

We can use the marginal inverseCDFs to map from (u, v) to(F −1

X (u), F −1Y (v)).

(F −1X (u), F −1

Y (v))

0

1t = FXY (F −1

X (u), F −1Y (v))

FXY (·, ·)

joint distribution function

Then map from (F −1X (u), F −1

Y (v)) to[0, 1] using the joint distributionfunction.

0

1t = C(u, v)

1

0 0 1

(u, v)

FXY

(F −1X , F −1

Y ) C

C(u, v) = FXY (F −1X (u), F −1

Y (v))

The copula function lets us mapdirectly from the unit square tothe joint distribution.

It lets us express the jointprobability as a function of themarginal distributions.

FXY (x , y) = C (FX (x), FY (y))

33 / 41

Page 39: Copula and multivariate dependencies for risk models

Understanding the copula function

X

Y

x

y

0

1t

FXY (x , y) = t

joint distribution function

FXY (x , y) = t is the probability thatX < x and Y < y

FX (x)

FY (y)(x, y)

We can use the marginal CDFs tomap from (x , y) to a point (u, v)on the unit square.

1

0 0 1

(u, v)F −1X (·)

F −1Y (·)

(F −1X (u), F −1

Y (v))

We can use the marginal inverseCDFs to map from (u, v) to(F −1

X (u), F −1Y (v)).

(F −1X (u), F −1

Y (v))

0

1t = FXY (F −1

X (u), F −1Y (v))

FXY (·, ·)

joint distribution function

Then map from (F −1X (u), F −1

Y (v)) to[0, 1] using the joint distributionfunction.

0

1t = C(u, v)

1

0 0 1

(u, v)

FXY

(F −1X , F −1

Y ) C

C(u, v) = FXY (F −1X (u), F −1

Y (v))

The copula function lets us mapdirectly from the unit square tothe joint distribution.

It lets us express the jointprobability as a function of themarginal distributions.

FXY (x , y) = C (FX (x), FY (y))

33 / 41

Page 40: Copula and multivariate dependencies for risk models

Multivariate simulation…

X

Y

1

0 0 1

We generate random points on[0, 1]² using the copula functionrandom generator.

F −1X (x)

F −1Y (y)

(x, y)

We use the inverse CDFs togenerate red points in the spaceof our real variables.

The joint distribution of the redpoints has marginals FX and FY ,with the required dependencystructure.

34 / 41

Page 41: Copula and multivariate dependencies for risk models

Multivariate simulation…

X

Y

1

0 0 1

We generate random points on[0, 1]² using the copula functionrandom generator.

F −1X (x)

F −1Y (y)

(x, y)

We use the inverse CDFs togenerate red points in the spaceof our real variables.

The joint distribution of the redpoints has marginals FX and FY ,with the required dependencystructure.

34 / 41

Page 42: Copula and multivariate dependencies for risk models

Simulating dependent random vectors

Various situations in practice where we might wish to simulatedependent random vectors (X1, …,Xn)

t :

▷ finance: simulate the future development of the values ofassets in a portfolio, where we know these assets to bedependent in some way

▷ insurance: “multi-line products” where payouts are triggeredby the occurrence of losses in one or more dependent businesslines, and wish to simulate typical losses

▷ environmental modelling: measures such as wind speed,temperature and atmospheric pressure are correlated

35 / 41

Page 43: Copula and multivariate dependencies for risk models

Simulation of correlated stock returns

(Coming back to our estimation of VaR of a CAC40/DAX stock portfolio)

Simulation using the following parameters:

▷ CAC: student-t distribution with tμ =0.000505, tσ = 0.008974, df = 2.768865

▷ DAX: student-t distribution with tμ =0.000864, tσ = 0.008783, df = 2.730707

▷ dependency: t copula with ρ=0.9413, df =2.8694

A s s u m p t i on : t h e

c o r r e l a t i o ns t r u c t u r e d

o e s

n o t c h a n ge w i t h t i m

e

36 / 41

Page 44: Copula and multivariate dependencies for risk models

VaR of a CAC-DAX portfolio

▷ 10 M€ portfolio, equally weightedbetween CAC and DAX indexes• CAC: daily returns with Student’s t with

tμ = 0.000505, tσ = 0.008974, df = 2.768865

• DAX: daily returns with Student’s t withtμ = 0.000864, tσ = 0.008783, df = 2.730707

• Dependency between CAC and DAXindexes modelled using a Student t copulawith ρ=0.9413, df=2.8694

▷ Monte Carlo simulation of portfolioreturns

▷ 30-day VaR(0.99) is 1.95 M€

0 2 4 6 8 10 12 14 16 180.0

0.1

0.2

0.3

0.4

0.5

0.6 Histogram of CAC/DAX portfolio value after 30 days

Initial portfolio value: 10.0

Mean final portfolio value: 10.23

30-day VaR(0.99): 1.954

D o w n l o a dt h e a s s o c i a

t e d

P y t h o n n ot e b o o k a t

risk-engineering.org

37 / 41

Page 45: Copula and multivariate dependencies for risk models

VaR of a CAC-AORD portfolio

▷ 10 M€ portfolio, equally weighted betweenCAC and AORD indexes• CAC: daily returns with Student’s t with tμ =

0.000505, tσ = 0.008974, df = 2.768865

• AORD: daily returns with Student’s t with tμ =0.0007309, tσ = 0.0082751, df = 3.1973

• Dependency between CAC and AORD indexesmodelled using a Student t copula withρ=0.3101, df=2.795

▷ Monte Carlo simulation of portfolio returns

▷ 30-day VaR(0.99) is 1.37 M€

▷ Lower than for CAC-DAX portfoliobecause of lower degree of dependency!

7 8 9 10 11 12 13 14 15 160.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7 Histogram of CAC/AORD portfolio value after 30 days

Initial portfolio value: 10.0

Mean final portfolio value: 10.20

30-day VaR(0.99): 1.375

38 / 41

Page 46: Copula and multivariate dependencies for risk models

VaR of a CAC-HSI portfolio

▷ 10 M€ portfolio, equally weighted betweenCAC and HSI indexes• CAC: daily returns with Student’s t with tμ =

0.000505, tσ = 0.008974, df = 2.768865

• HSI: daily returns with Student’s t with tμ =0.000988, tσ = 0.01032, df = 2.269018

• Dependency between CAC and DAX indexesmodelled using a Student t copula withρ=0.35695, df=2.542247

▷ Monte Carlo simulation of portfolio returns

▷ 30-day VaR(0.99) is 2.23 M€

▷ Higher than for CAC-DAX portfoliodespite lower degree of dependency (why?)

2 4 6 8 10 12 14 16 180.0

0.1

0.2

0.3

0.4

0.5 Histogram of CAC/HSI portfolio value after 30 days

Initial portfolio value: 10.0

Mean final portfolio value: 10.25

30-day VaR(0.99): 2.227

39 / 41

Page 47: Copula and multivariate dependencies for risk models

Further reading

▷ Teaching material by Prof. Paul Embrecht from ETH Zurich, an importantresearcher in the use of copula techniques in finance: qrmtutorial.org

▷ Article ‘The Formula That Killed Wall Street’? The Gaussian Copula and theMaterial Cultures of Modelling by Donald MacKenzie and Taylor Spears

▷ Slides on extreme and correlated risks by Prof. Arthur Charpentier:perso.univ-rennes1.fr/arthur.charpentier/slides-edf-2.pdf

For more free course materials on risk engineering,visit https://risk-engineering.org/

40 / 41

Page 48: Copula and multivariate dependencies for risk models

Feedback welcome!

Was some of the content unclear? Which parts of the lecturewere most useful to you? Your comments [email protected] (email) or@LearnRiskEng (Twitter) will help us to improve these coursematerials. Thanks!

@LearnRiskEng

fb.me/RiskEngineering

google.com/+RiskengineeringOrgCourseware

This presentation is distributed under the terms ofthe Creative Commons Attribution – Share Alikelicence

For more free course materials on risk engineering,visit https://risk-engineering.org/

41 / 41