ARCH and GARCH. Modeling Volatility Dynamics

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Modeling Unequal Variability Equal Variability: Homoscedasticity Unequal Variability: Heteroscedasticity Means any

Modeling Unequal Variability

Equal Variability: Homoscedasticity
Unequal Variability: Heteroscedasticity
Means any variability (around the

mean) that is not homoscedasticity
Models must be developed for specific cases
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What These Acronym Mean? ARCH Autoregressive Conditional Heteroscedasticity GARCH Generalized ARCH

What These Acronym Mean?

ARCH
Autoregressive Conditional Heteroscedasticity
GARCH
Generalized ARCH

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Information in e2 Let εt have the mean 0 and the

Information in e2

Let εt have the mean 0 and the variance

σt.
Let et be the residual of a model fitted.
Then:
et estimates εt
et2 estimates the variance σt2.
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ARCH Modeling of σt2. ARCH(1) ARCH as AR(1) on

ARCH Modeling of σt2.

ARCH(1)
ARCH as AR(1) on

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GARCH GARCH(1) GARCH (1) as ARMA(1,1) on

GARCH

GARCH(1)
GARCH (1) as ARMA(1,1) on

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Asymmetry in GARCH - TARCH TARCH(1,1) d = 1 if εt 0

Asymmetry in GARCH - TARCH

TARCH(1,1)

d = 1 if εt < 0,

and = 0 if εt > 0
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Asymmetry in GARCH - EGARCH EGARCH(1,1)

Asymmetry in GARCH - EGARCH

EGARCH(1,1)