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Re: st: Testing equality of 2 coefficients after FE regression: How does Stata compute the Pooled SE and test statistic?


From   andreas nordset <andreas.nordset@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Testing equality of 2 coefficients after FE regression: How does Stata compute the Pooled SE and test statistic?
Date   Wed, 8 Dec 2010 17:32:26 +0100

Yes, that makes sense. Thanks  a lot!

On Wed, Dec 8, 2010 at 11:57 AM, Maarten buis <maartenbuis@yahoo.co.uk> wrote:
> --- On Wed, 8/12/10, andreas nordset  wrote:
>> after estimating a FE model, I am testing the equality of
>> two coefficients.
>>
>> The difference between them is about 3000 and the SE in the
>> regression output are respectively 1700 and 1600. I would
>> thus have thought that the test statistic should be
>> t = 3000/sqrt(1700^2+1600^2) =1.29
>
> You are missing the covariance of the joint sampling
> distribution of these two parameters. The variance of the
> difference is: var(x1) + var(x2) - 2*cov(x1,x2)
>
> Hope this helps,
> Maarten
>
> --------------------------
> Maarten L. Buis
> Institut fuer Soziologie
> Universitaet Tuebingen
> Wilhelmstrasse 36
> 72074 Tuebingen
> Germany
>
> http://www.maartenbuis.nl
> --------------------------
>
>
>
>
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