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Re: st: Interaction and constraint


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Interaction and constraint
Date   Sun, 2 Jan 2011 20:42:21 +0000 (GMT)

--- On Sun, 2/1/11, Shige Song wrote:
> . use http://www.stata-press.com/data/r11/fvex
> . regress y i.group group#c.age
<snip> 
> Now I want to simply the model by constrainning the second
> (2.group#c.age) and the third terms (3.group#c.age) to be
> equal (suppose that will improve the model fit), how should
> I do this?
> 
> In addition, assume this is a longitudinal data analysis
> situation and I am estimating a population average model
> using "xtlogit, pa", can I constrain the two terms to be equal?

I am old fashioned, I tend to impose constraints by creating
new variables.

*---------------- begin example ----------------
use http://www.stata-press.com/data/r11/fvex
gen group2 = group
recode group2 (3=2)
regress y i.group i.group2#c.age
*----------------- end example -----------------
(For more on examples I sent to the Statalist see: 
http://www.maartenbuis.nl/example_faq )

You can use the same trick for -xtlogit-.

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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