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st: Re: pooled vs panel data

From   Kit Baum <>
Subject   st: Re: pooled vs panel data
Date   Sat, 22 Jul 2006 09:00:15 -0400

If you mean that you did

regress y x1 x2 x3
xtreg y x1 x2 x3, fe

and the F-test at the foot of xtreg said that there are significant differences between the intercepts for the units of the panel, then the pooled OLS regression involves placing a number of inappropriate constraints on the fixed effects regression. When you place binding constraints on a regression, the coefficients change. When those constraints are soundly rejected by the data, it is a bad idea.

Kit Baum, Boston College Economics

On Jul 22, 2006, at 2:33 AM, Jeff wrote:

I ran a few MLE regressions and set them up first as pooled data and second
as panel data. The regression coefficients were almost identical, only a
variation of a few decimal points, and the standard errors were much lower
in the panel regression. I was expecting the coefficients to still be an
unbiased estimate in both regressions, but I expected that they should be
slightly different from each other. Is this unusual?
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