Problem with estimation results of ARMAX-GARCHX

Dear Alexios,

thank you for your help. Now, I get decent results for AR and MA part from
ugarchfit. These are approximately the same as for arima(). Nevertheless,
the results for the exogenous variables added are still different between
the two functions.

I attachted the data in a .csv file.

Regards,

Philipp

-----Urspr?ngliche Nachricht-----
Von: alexios ghalalanos [mailto:alexios at 4dscape.com] 
Gesendet: Donnerstag, 18. September 2014 10:01
An: Philipp Lammers; r-sig-finance at r-project.org
Cc: alexios at 4dscape.com
Betreff: Re: [R-SIG-Finance] Problem with estimation results of ARMAX-GARCHX

Philipp,

In the presence of heteroscedasticity, there is a loss in the asymptotic
efficiency of the parameter estimates which are no longer BLUE (see the
original ARCH paper by Engle 1982). This effectively means that for most
datasets of length N (where N is some finite number), the parameters will be
somewhat different.
In the rugarch package, ARMA-GARCH is jointly estimated.

If you want to compare non-GARCH ARMA with the typical arima function in R,
use the arfimaspec/arfimafit functions (or set the ugarchspec garchOrder to
c(0,0) and the stationarity flag in the fit.control to 0).
You should also choose method="ML" for arima.

Regards,

Alexios

PS I could not download your dataset from dropbox (only the code).

Hello everybody,

 

I am currently facing an estimation problem in the ARMAX-GARCHX model. 
The "rugarch"-package is used for estimation. The problem arises 
because my professor is not satisfied with the estimation results, he 
expects the ARMAX-GARCH results in the mean equation to be the same as 
the normal ARMAX results. But this is not the case and the results differ

significantly.

 

I already wrote to the programmer of the rugarch package, who 
thankfully gave me a hint , that the results are different under the 
presence of heteroskedasticity. He recommended me to post to this 
mailing list. Can anybody confirm that the results are different? 
Where can I find this issue in the literature?

 

My R-code can be downloaded from my Dropbox:
https://www.dropbox.com/s/k557ev4lmmnykqu/ARMAGARCH.R?dl=0 .Note that 
the corresponding data will be downloaded from the Dropbox as well, 
when the code is executed.

 

I hope that you can help me.

 

Thank you all in advance.

 

Philipp Lammers

 


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