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st: Re: Problem with xttest2

From   Kit Baum <>
To   "Elisabeth Kutschka" <>
Subject   st: Re: Problem with xttest2
Date   Fri, 5 Mar 2010 10:11:09 -0500

The reason for that is usually that you have more units in the panel than observations on each unit. That would cause -sureg- to fail with a singular VCE of the residuals, and as this test is looking at that VCE, it cannot handle it either. A matrix with g columns cannot have full column rank if it has fewer then g rows, and in this case the xtgls residuals form such a matrix.


On Mar 5, 2010, at 9:18 AM, Elisabeth Kutschka wrote:

> Dear Mr. Baum,
> I used your STATA module "xttest2" to perform Breusch-Pagan LM test for
> cross-sectional correlation after xtgls-Regression. (I use STATA 10)
> However, the test does not work and the error message is: "Correlation
> matrix of residuals is singular. not possible with test r(131)".
> Is there any way to solve this problem? Thank you very much for your help!
> With best regards,
> Elisabeth Kutschka
> ______________________________
> Dipl.-Vw. Elisabeth Kutschka
> Otto-von-Guericke-Universität Magdeburg
> Lehrstuhl für Internationale Wirtschaft
> Postfach 4120
> D-39106 Magdeburg
> Tel.: (49)391 67 11 645
> Fax: (49)391 67 11 177

Kit Baum   |   Boston College Economics & DIW Berlin   |
                              An Introduction to Stata Programming  |
   An Introduction to Modern Econometrics Using Stata  |

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