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RE: st: RE: Unordered Categorical Predictor Variable


From   "Cohen, Elan" <cohened@upmc.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: RE: Unordered Categorical Predictor Variable
Date   Fri, 25 Jan 2013 14:15:55 +0000

Louis,

You'll be interested in the postestimation command -test- and maybe -margins-.  Also, you no longer need to use the -xi:- prefix.

sysuse auto
reg price i.rep78
test 2.rep78=3.rep78

HTH,

- Elan


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of louis grandjean
Sent: Thursday, January 24, 2013 19:34
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: RE: Unordered Categorical Predictor Variable

Thanks Peter for your help.  I'm sure you're not missing the point.  I
may be however.  If I use the i.varname command with xi: then I will
get the odds ratio reported for one comparison of interest, i.e.
bacterial family 1 vs bacterial family 2,3 & 4 as the reference.  I
also want to know the odds ratio for bacterial family 2 vs 1,3 & 4.
Could I just run the regression again having changed the base
reference, or is there some way I can do it in the one command.



On 24 January 2013 18:48, Lachenbruch, Peter
<Peter.Lachenbruch@oregonstate.edu> wrote:
> i may be missing the point here, but why cant you use the factor variable coding (i.varname)  you can vary the base variable.  See factor variable in manual.  comparing all possible factor codings doesn't make much sense since they will be dependent, and you can use contrasts for whatever you want.
>
> Peter A. Lachenbruch,
> Professor (retired)
> ________________________________________
> From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] on behalf of louis grandjean [lgrandjean@gmail.com]
> Sent: Thursday, January 24, 2013 7:08 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: Unordered Categorical Predictor Variable
>
> Dear Statalist,
>
> I'm using Stata 11 and am struggling with how to best analyse an
> unordered categorical predictor in a logistic regression.
>
> My categorical predictor is "bacterial family" so it doesn't make
> sense to always compare one family to an arbitrarily chosen reference
> family.  What I want to do is compare each family in turn to all the
> other families.
>
> I think deviation coding would give me one family vs the mean of all
> the families, but I want to get one family vs the other famlies, and
> obtain an odds ratio for each level.
>
> I've looked at xi3 but this doesn't seem to answer the problem.
>
> I'd be very grateful for your thoughts.
>
> Best wishes Louis
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