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# st: Autocorrelation after xtdpdsys

 From Angela C To statalist@hsphsun2.harvard.edu Subject st: Autocorrelation after xtdpdsys Date Fri, 1 Feb 2013 03:20:27 +0200

```I am using xtdpdsys to estimate a panel with N=27 and T=17.

the results come out as follows

xtdpdsys Deb Gr INT, lags(1) vce(robust) artests(2)

System dynamic panel-data estimation         Number of obs         =       430
Group variable: CTY                          Number of groups      =        27
Time variable: Year
Obs per group:    min =        14
avg =  15.92593
max =        16

Number of instruments =    138               Wald chi2(3)          =    677.64
Prob > chi2           =    0.0000
One-step results
------------------------------------------------------------------------------
|               Robust
Deb |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
Deb |
L1. |   1.091666   .0627754    17.39   0.000     .9686287    1.214704
|
Gr |  -104.3667   16.53084    -6.31   0.000    -136.7665   -71.96683
INT |   -1.38898   .4177452    -3.32   0.001    -2.207746   -.5702147
_cons |   2.437429   2.130174     1.14   0.253    -1.737636    6.612494
------------------------------------------------------------------------------
Instruments for differenced equation
GMM-type: L(2/.).Deb
Standard: D.Gr D.INT
Instruments for level equation
GMM-type: LD.Deb
Standard: _cons

I then run the Arellano-Bond postestimation test and stata returns:

Arellano-Bond test for zero autocorrelation in first-differenced errors
+-----------------------+
|Order |  z     Prob > z|
|------+----------------|
|   1  |-3.4443  0.0006 |
|   2  |-.37263  0.7094 |
+-----------------------+
H0: no autocorrelation

According to my model, the 2nd order autocorrelation appearing in the
test has been corrected by the programme (I set artests(2))?

If it was not corrected, is there a way to correct it afterwards and
take new, corrected coefficients?

Thank you.
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```