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Re: st: areg drops year dummies

From   Maarten Buis <>
Subject   Re: st: areg drops year dummies
Date   Mon, 16 Jul 2012 16:24:12 +0200

On Mon, Jul 16, 2012 at 4:00 PM, Ozgur Ozdemir wrote:
> i am using areg in my pooled data  set with year dummies such as xi:areg y x1 x2 i.year, absorb(industry) but some of the years not only the first one such as 2000, 2001, 2002, 2008 etc are dropped. can anybody advice why this might happen ?

That means there is some perfect colinearity going on. I would look
for very small industries and merge those with adjacent or similar

Also, the -xi- prefix is outdated. Since you have not said otherwise I
will assume --- per the Statalist FAQ --- that you have Stata 12. In
that case you should leave the -xi- prefix out. If you have Stata <
12: read the FAQ, a link can be found at the bottom of every post on

-- Maarten

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
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