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Time Series Volatility Models
-Different volatility estimation by
Equal Weight Model & EWMA & GARCH(1,1)
-By Di Wu & Zheng Rong
Agenda:
 Equal Weight model
 EWMA
 GARCH(1,1)
Different volatility estimation by EWMA and Equal weight
model
We estimate the current
volatility by
is the daily return on
day i.
We estimate the current
volatility by
 Constant Volatility is
far from perfect
 Volatility, like assets
price, is a stochastic
process
 Attempted to keep
track the changing of
volatility
Equal weight modelImportance of Volatility EWMA(exponentially
weight)
Four-Index Example
Portfolio
 Dow Jones $ 4
million
 FTSE 100 $ 3
million
 CAC 40 $ 1
million
 Nikkei 225 $ 2
million
Initial Data
Data is from 07/08/2006
to 25/09/2008, totally
501 days with 500 daily
returns.
Find Volatility
We are going to
estimate the volatility
on tomorrow,
26/09/2008.
Comparing the results
from two models.
Equal weight
model  Calculate daily returns
 Find variance-corvariance
matrix by
 From the matrix, we could find
portfolio Std. Thus, we find one
day 99% VaR is $217,757
Process:
EWMA(exponentially
weight)  Calculate daily returns
 Find variance-corvariance
matrix by
 From the matrix, we could find
portfolio Std. Thus, we find one
day 99% VaR is $471,025
Process:
--path of volatility^2 from day 1 to day 501
Results
 Sheets show the estimated
daily standard deviations are
much higher when EWMA is
used than data are equally
weighted.
 Recall:
 This is because volatilities
were much higher during the
period immediately preceding
September 25, 2008, than
during the rest of the 500
Covariance matrix of equal weight model
Covariance matrix of EWMA
GARCH(1,1)
Mean Reverting
Estimating GARCH(1,1) parameters
Solver!
How Good is the
Model?
 Remove
Autocorrelation
 LjungBox statistic
 where is the
autocorrelation for a
lag of k, K is the
number of lags
For K =15
zero
autocorrelation
Can be
rejected
>=25
S&P 500
3/31/114/29/16
sn
2
=0.0000043556+0.7993un-1
2
+0.153719sn-1
2
Long Run Volatility Per
Year : 0.1528
Ljung-Box: 26.25
Compare GARCH
to VIX
VIX: Implied Volatility
of S&P 500 index
options
GRACH: sqrt(252)*
GRACH(1,1) vol per
day
Forecasting Future Volatility
May-2-2016
se
=0.0000927+(0.7993+0.1537)*(0.00004286-0.0000927)
10.67 GRACH vol vs 15.05 implied vol
Long run volatility per year 15.28
Summary
 The key feature of the EWMA is
that it does not give equal weight
to the observations on the ui^2 .
 The more recent an observation,
the greater the weight assigned
to it.
 GARCH(1,1) incorporates mean
reversion ------theoretically more
appealing
Which model is better?
Thank you
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Math 5076 Project 2

  • 1. Time Series Volatility Models -Different volatility estimation by Equal Weight Model & EWMA & GARCH(1,1) -By Di Wu & Zheng Rong
  • 2. Agenda: Equal Weight model EWMA GARCH(1,1)
  • 3. Different volatility estimation by EWMA and Equal weight model We estimate the current volatility by is the daily return on day i. We estimate the current volatility by Constant Volatility is far from perfect Volatility, like assets price, is a stochastic process Attempted to keep track the changing of volatility Equal weight modelImportance of Volatility EWMA(exponentially weight)
  • 4. Four-Index Example Portfolio Dow Jones $ 4 million FTSE 100 $ 3 million CAC 40 $ 1 million Nikkei 225 $ 2 million Initial Data Data is from 07/08/2006 to 25/09/2008, totally 501 days with 500 daily returns. Find Volatility We are going to estimate the volatility on tomorrow, 26/09/2008. Comparing the results from two models.
  • 5. Equal weight model Calculate daily returns Find variance-corvariance matrix by From the matrix, we could find portfolio Std. Thus, we find one day 99% VaR is $217,757 Process:
  • 6. EWMA(exponentially weight) Calculate daily returns Find variance-corvariance matrix by From the matrix, we could find portfolio Std. Thus, we find one day 99% VaR is $471,025 Process: --path of volatility^2 from day 1 to day 501
  • 7. Results Sheets show the estimated daily standard deviations are much higher when EWMA is used than data are equally weighted. Recall: This is because volatilities were much higher during the period immediately preceding September 25, 2008, than during the rest of the 500 Covariance matrix of equal weight model Covariance matrix of EWMA
  • 10. How Good is the Model? Remove Autocorrelation LjungBox statistic where is the autocorrelation for a lag of k, K is the number of lags For K =15 zero autocorrelation Can be rejected >=25
  • 12. Compare GARCH to VIX VIX: Implied Volatility of S&P 500 index options GRACH: sqrt(252)* GRACH(1,1) vol per day
  • 13. Forecasting Future Volatility May-2-2016 se =0.0000927+(0.7993+0.1537)*(0.00004286-0.0000927) 10.67 GRACH vol vs 15.05 implied vol Long run volatility per year 15.28
  • 14. Summary The key feature of the EWMA is that it does not give equal weight to the observations on the ui^2 . The more recent an observation, the greater the weight assigned to it. GARCH(1,1) incorporates mean reversion ------theoretically more appealing Which model is better?

Editor's Notes

  • #9: The parameter belta can be interpreted as a decay rate. It is similar to in the EWMA model. But the GARCH(1,1) assigs weights that decline exponentially to past u^2, it also assigns some weight to the long-run average volatility. The GARCH (1,1) model recognizes that over time the variance tends to get pulled back to a long-run average level of VL. In practice, variance rates do tend to be mean reverting. The GARCH(1,1) model incorporates mean reversion, whereas the EWMA model does not. GARCH (1,1) is therefore theoretically more appealing than the EWMA model.
  • #10: We are interested in choosing omega, alpha, and belta to maximize the sum of the numbers in the sixth column. This involves an iterative search procedure. Occasionally Solver gives a local maximum, so testing a number of different starting values for parameters is a good idea.
  • #11: Informally, it is the similarity between observations as a function of the time lag. considering the autocorrelation structure for the variables u_i^2 / sigma_i^2 Autocorrelation of the errors violates the ordinary least squares (OLS) assumption that the error terms are uncorrelated, meaning that the油Gauss Markov theorem油does not apply, and that OLS estimators are no longer the Best Linear Unbiased Estimators (BLUE). DurbinWatson statistic