Modelling Dependence with Copulas - IFOR
Modelling Dependence with Copulas - IFOR
Modelling Dependence with Copulas - IFOR
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4.2 The Marshall-Olkin Family<br />
Marshall-Olkin<br />
Y<br />
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0.0 0.2 0.4 0.6 0.8 1.0<br />
X<br />
Figure 4.1: Samples from the Marshall-Olkin copula. λ 1 =1.1,λ 2 =0.2 andλ 12 =<br />
0.6<br />
Using the result in Theorem 3.3 and the theorem above yields:<br />
∫∫<br />
τ α1,α 2<br />
= 4 C α1,α 2<br />
(u, v)dC α1,α 2<br />
(u, v) − 1<br />
I<br />
( 2 ∫∫ 1<br />
= 4<br />
2 − ∂<br />
I ∂u C α 1,α 2<br />
(u, v) ∂<br />
)<br />
∂u C α 1,α 2<br />
(u, v)du dv − 1<br />
= ...<br />
2<br />
α 1 α 2<br />
=<br />
.<br />
α 1 + α 2 − α 1 α 2<br />
Thus all values in the interval [0, 1] can be obtained for ρ α1,α 2<br />
and τ α1,α 2<br />
. The<br />
Marshall-Olkin copulas have upper tail dependence. Without loss of generality<br />
assume that α 1 >α 2 .<br />
C(u, u)<br />
lim<br />
u→1− 1 − u<br />
1 − 2u + u 2 min(u −α1 ,u −α2 )<br />
= lim<br />
u→1−<br />
1 − u<br />
1 − 2u + u 2 u −α2<br />
= lim<br />
u→1− 1 − u<br />
= lim (2 − + α<br />
u→1− 2u1−α2 2 u 1−α2 )=α 2 ,<br />
and hence<br />
λ U =min(α 1 ,α 2 ).<br />
We now present the natural multivariate extension of the bivariate Marshall-<br />
Olkin family.<br />
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