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statistique, théorie et gestion de portefeuille - Docs at ISFA

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140 4. Relax<strong>at</strong>ion <strong>de</strong> la vol<strong>at</strong>ilité<br />

∫ dt E[σ(t) | ω 0 ] − E[σ(t)]<br />

10 −1<br />

10 −2<br />

10 0<br />

Nikkei 250 : Aug 19, 1991<br />

S&P 500 : Aug 19, 1991<br />

FT−SE 100 : Aug 19, 1991<br />

CAC 40 : Sep 11, 2001<br />

S&P 500 : Oct 19, 1987<br />

10 1<br />

Time (trading days)<br />

Slope α = 1/2<br />

August 19, 1991 : Putsh against Presi<strong>de</strong>nt Gorbachev<br />

September 11, 2001: Attack against the WTC<br />

Figure 1: Cumul<strong>at</strong>ive excess vol<strong>at</strong>ility <strong>at</strong> scale ∆t, th<strong>at</strong> is, integral over time of Eexo[σ 2 (t) | ω0] − σ 2 (t),<br />

due to the vol<strong>at</strong>ility shock induced by the coup against Presi<strong>de</strong>nt Gorbachev observed in three British,<br />

Japanese and USA indices and the shock induced by the <strong>at</strong>tack of September 11, 2002 against the World<br />

Tra<strong>de</strong> Center. The dashed line is the theor<strong>et</strong>ical prediction obtained by integr<strong>at</strong>ing (1), which gives a ∝ √ t<br />

time-<strong>de</strong>pen<strong>de</strong>nce. The cumul<strong>at</strong>ive excess vol<strong>at</strong>ility following the crash of October 1987 is also shown with<br />

circles. Notice th<strong>at</strong> the slope of the non-constant curve for the October 1987 crash is very different from the<br />

value 1/2 expected and observed for exogeneous shocks. This crash and the resulting vol<strong>at</strong>ility relax<strong>at</strong>ion<br />

can be interpr<strong>et</strong>ed as an endogeneous event.<br />

4<br />

10 2

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