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st: RE: Reference Category for Dummy Variables


From   "David Harrison" <David@icnarc.org>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Reference Category for Dummy Variables
Date   Fri, 8 Oct 2004 08:56:44 +0100

If you are entering your 0/1 dummy variable directly into the logistic regression, then Stata does not "know" it is a dummy and treats it as it would any linear term... in other words the "reference category" will be 0 (as beta*0 = 0) and the odds ratio quoted will be for the category 1 (as beta*1 = beta).

If, on the other hand, you are (unnecessarily) using -xi- to declare your variable as a dummy then the default action will still be to omit the zero category (the first numerically or alphabetically) but this can be changed with -char varname[omit] #- or -char varname[omit] "string"- depending on the storage type... see the help for -xi-.

Hope this clarifies things for you.

David
david@icnarc.org

-----Original Message-----
From: Carter Ivan Rees [mailto:CRees1@uwyo.edu]
Sent: 07 October 2004 21:18
To: statalist@hsphsun2.harvard.edu
Subject: st: Reference Category for Dummy Variables


I am running a logistic regression and would like to know which category of a 0/1 dummy variable Stata uses as the reference category (first or last).    The results I am getting right now are counter intuitive.   I have checked my coding scheme and it is OK.  Thanks in advance.

*******************************************
Carter Rees, M.A.
Associate Research Scientist
Wyoming Survey & Analysis Center
710 Garfield St.
Suite 320
Laramie, WY 82072
307-399-0496
*******************************************



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