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THE EXPONENTIAL GARCH MODEL. THE EXPONENTIAL GARCH MODEL. To allow for asymmetric effects between positive and negative asset returns, he considers the weighted innovation where θ and γ are real constants
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THE EXPONENTIAL GARCH MODEL • To allow for asymmetric effects between positive and negative asset returns, he considers the weighted innovation • where θ and γ are real constants • Both t and | t | − E(|t |) are zero-mean iidsequences with continuous distributions
Therefore E[g(t )] = 0 • The asymmetry of g(t ) can easily be seen by rewriting it as
An EGARCH(m, s) model can be written as • where α0 is a constant • B is the back-shift (or lag) operator such that Bg(t ) =g(t−1)
The use of g( t ) enables the model to respond asymmetrically to positive and negative lagged values of at
To better understand the EGARCH model, let us consider the simple model with order (1, 0)
Example • We consider the monthly log returns of IBM stock from January 1926 to December 1997 for 864 observations. • An AR(1)-EGARCH(1, 0) model is entertained and the fitted model is