FRM Part I · FRM Exam Part I · Measuring and Monitoring Volatility
Compared with an EWMA model with lambda = 0.94, a GARCH(1,1) model with omega > 0 and alpha + beta < 1 differs mainly in that it:
GARCH(1,1) with a positive omega and persistence below one pulls variance back toward a long-run level, whereas EWMA is a special case with omega of zero and persistence of one, so it has no mean reversion.
- AIncorporates a mean-reverting long-run variance termCorrect
- BAssigns equal weights to all past squared returns
- CGives zero weight to the most recent squared return
- DCannot be estimated by maximum likelihood
Explanation
EWMA is a special case of GARCH with omega = 0 and alpha + beta = 1, so it has no mean reversion. GARCH with omega > 0 adds a long-run variance anchor. Both give declining weights to past returns, both use the latest return, and GARCH is estimated by maximum likelihood.
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