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Re: st: How to constraint the sum of the coefficients to zero for a factor variable.


From   Maarten Buis <maartenlbuis@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: How to constraint the sum of the coefficients to zero for a factor variable.
Date   Fri, 5 Aug 2011 14:19:42 +0200

On Fri, Aug 5, 2011 at 1:28 PM, Sam Brilleman wrote:
> Does anyone know how to change the constraint on the coefficients for 'var4'
> so that the sum of the coefficients is zero (i.e. sum(b4i) = 0) rather than
> treating one of the factor levels as a reference category (i.e. b4i = 0 for
> some given i). Note that the latter is the standard parameter constraint
> used by STATA's estimation commands.

I don't know of a way to do this in Stata's factor variable notation.
You can however create the necesary variables using -xi3-, where they
are called "effect coding", see -findit xi3-.

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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