Hi, everyone, 
   I used the data in the attachment to run ARCH (2) and GARCH (0,2), i assumed 
they would give me the same result but they did not. 
 I have the result showing in below:
ARCH (2)
arch 2 re const

Model 1: WLS (ARCH), using observations 3-7837 (n = 7835)
Dependent variable: re
Variable used as weight: 1/sigma

             coefficient   std. error    t-ratio    p-value 
  ----------------------------------------------------------
  const      0.000515703   0.000109897    4.693    2.74e-06  ***

  alpha(0)   8.11556e-05   6.06157e-06   13.39     1.96e-40  ***
  alpha(1)   0.225945      0.0109590     20.62     5.15e-92  ***
  alpha(2)   0.243682      0.0109590     22.24     2.85e-106 ***

Statistics based on the weighted data:

Sum squared resid    6676.296   S.E. of regression   0.923158
R-squared            0.000000   Adjusted R-squared   0.000000
Log-likelihood      −10490.44   Akaike criterion     20982.87
Schwarz criterion    20989.84   Hannan-Quinn         20985.26

Statistics based on the original data:

Mean dependent var   0.000487   S.D. dependent var   0.012371
Sum squared resid    1.198934   S.E. of regression   0.012371


GARCH ( 0,2)
Model 2: GARCH, using observations 1-7837
Dependent variable: re
Standard errors based on Hessian

             coefficient   std. error    t-ratio    p-value 
  ----------------------------------------------------------
  const      0.00104076    9.69109e-05    10.74    6.65e-27  ***

  alpha(0)   4.16523e-05   1.26856e-06    32.83    1.91e-236 ***
  alpha(1)   0.400826      0.0222482      18.02    1.46e-72  ***
  alpha(2)   0.437669      0.0224141      19.53    6.53e-85  ***

Mean dependent var   0.000486   S.D. dependent var   0.012370
Log-likelihood       25033.25   Akaike criterion    −50056.50
Schwarz criterion   −50021.67   Hannan-Quinn        −50044.57

Unconditional error variance = 0.000257901
Likelihood ratio test for (G)ARCH terms:
  Chi-square(2) = 3457.91 [0]



the Code i used is 
open nasdaq.dat
arch 2 re const
garch 0 2; re 


Can anyone help me explain why they are not the same?
                                          
Hi, everyone,
   I used the data in the attachment to run ARCH (2) and GARCH (0,2), i assumed they would give me the same result but they did not.
 I have the result showing in below:
ARCH (2)
arch 2 re const

Model 1: WLS (ARCH), using observations 3-7837 (n = 7835)
Dependent variable: re
Variable used as weight: 1/sigma

             coefficient   std. error    t-ratio    p-value
  ----------------------------------------------------------
  const      0.000515703   0.000109897    4.693    2.74e-06  ***

  alpha(0)   8.11556e-05   6.06157e-06   13.39     1.96e-40  ***
  alpha(1)   0.225945      0.0109590     20.62     5.15e-92  ***
  alpha(2)   0.243682      0.0109590     22.24     2.85e-106 ***

Statistics based on the weighted data:

Sum squared resid    6676.296   S.E. of regression   0.923158
R-squared            0.000000   Adjusted R-squared   0.000000
Log-likelihood      −10490.44   Akaike criterion     20982.87
Schwarz criterion    20989.84   Hannan-Quinn         20985.26

Statistics based on the original data:

Mean dependent var   0.000487   S.D. dependent var   0.012371
Sum squared resid    1.198934   S.E. of regression   0.012371


GARCH ( 0,2)
Model 2: GARCH, using observations 1-7837
Dependent variable: re
Standard errors based on Hessian

             coefficient   std. error    t-ratio    p-value
  ----------------------------------------------------------
  const      0.00104076    9.69109e-05    10.74    6.65e-27  ***

  alpha(0)   4.16523e-05   1.26856e-06    32.83    1.91e-236 ***
  alpha(1)   0.400826      0.0222482      18.02    1.46e-72  ***
  alpha(2)   0.437669      0.0224141      19.53    6.53e-85  ***

Mean dependent var   0.000486   S.D. dependent var   0.012370
Log-likelihood       25033.25   Akaike criterion    −50056.50
Schwarz criterion   −50021.67   Hannan-Quinn        −50044.57

Unconditional error variance = 0.000257901
Likelihood ratio test for (G)ARCH terms:
  Chi-square(2) = 3457.91 [0]



the Code i used is
open nasdaq.dat
arch 2 re const
garch 0 2; re


Can anyone help me explain why they are not the same?

Attachment: nasdaq.dat
Description: Binary data

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