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 <[email protected]> wrote:
> --- "E. Michael Foster" <[email protected]> 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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