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Re: st: problems with xi3


From   "Ben Jann" <ben.jann@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: problems with xi3
Date   Tue, 6 May 2008 09:33:31 +0200

Also see the -devcon- package on SSC (-ssc describe devcon-) which can
be used to "normalize" estimates that use the standard dummy coding.
Note that -devcon- also inserts the (redundant) coefficient for the
base category, which is useful if you want to compute the Oaxaca
decomposition.

By the way, I just completed a new version of the -oaxaca- package
that has this functionality built in. It should be available from SSC
shortly. Watch out for the announcement on this list.

ben

On Tue, Apr 15, 2008 at 12:01 PM, Maarten buis <maartenbuis@yahoo.co.uk> wrote:
> --- "E. Michael Foster" <mike4kids@gmail.com> wrote:
>  > I'm trying to impose the normalizing constraint on a set of dummy
>  > variables representing a set of mutually exclusive categories.
>  > A common identification constraint is to set the sum of the dummies
>  > to zero.
>
>  This constraint is sometimes referred to as effect coding, and is
>  already implemented in -xi3- so you do not need to add a user defined
>  contrast. When you do that, the results from a model using your
>  manually created variables correspond to the results from a model using
>  the variables created by -xi3-. See the example below:
>
>  *-------------- begin example ----------------
>  sysuse auto, clear
>
>
>  sort mpg
>  gen mpgg=group(3)
>  xi i.mpgg, prefix(D)
>  for var D*: replace X=-1 if mpgg==1
>  regress weight D*
>
>  xi3: reg weight e.mpgg
>  *------------- end example -------------------
>  (For more on how to use examples I sent to the Statalist, see
>  http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )
>
>  Hope this helps,
>  Maarten
>
>  -----------------------------------------
>  Maarten L. Buis
>  Department of Social Research Methodology
>  Vrije Universiteit Amsterdam
>  Boelelaan 1081
>  1081 HV Amsterdam
>  The Netherlands
>
>  visiting address:
>  Buitenveldertselaan 3 (Metropolitan), room Z434
>
>  +31 20 5986715
>
>  http://home.fsw.vu.nl/m.buis/
>  -----------------------------------------
>
>
>
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