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st: robust

From   Susie Enders <>
Subject   st: robust
Date   Sun, 14 May 2006 03:24:33 +0100 (BST)


I am running panel data regressions with 2-way fixed
effects, between companies and between years. I need
to obtain robust standard errors and t-statistics. The
problem is that when I try to use the robust command I
get an error message.

When I run the regression as follows it works fine:
xi:xtreg lnincome lnCA lnC1 lnC10 lnC15, fe

However when I add "robust" as follows:
. xi:xtreg lnincome lnCA lnC1 lnC10 lnC15, fe

I get the following output (in the first line it looks
as if it will give the regression output, but then
instead gives an error message that the robust option
is not allowed. The part about naturally coded,
_Idate_136 omitted can be ignored as it gives this
anyway without robust):            _Idate_136-183      (naturally
coded; _Idate_136 omitted)
option robust not allowed

I have tried studying the help files on robust, xtreg,
xtdata etc, but still do not understand the problem.
Is it impossible theoretically to get robust t stats
and standard errors with such a regression, or is it a
programming issue? (I did also read about clustering
but I was wondering if it is possible to get the
robust stats without that).

I would really appreciate any help, thanks!


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