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Re: st: Categorical variable in regression


From   Petya Alexandrova <p.alexandrova@montesquieu-instituut.nl>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Categorical variable in regression
Date   Wed, 23 Jan 2013 13:32:30 +0200 (EET)

In a regression with dummy variables one category is always omitted because it is the reference category. 
You can modify which category to be used as a reference group.

Petya 












 >-------- Оригинално писмо --------

 >От: John Ataguba johnataguba@yahoo.co.uk

 >Относно: st: Categorical variable in regression

 >До: Statalist statalist mailing <statalist@hsphsun2.harvard.edu>

 >Изпратено на: Сряда, 2013, Януари 23 13:22:09 EET



 
> Dear Statalist members
 
> 
 
> 
 
> I have a problem trying to let Stata display coefficients for all the categories of a categorical variable in a regression.
 
> 
 
> Consider the example below:
 
> 
 
> **********************************************
 
> clear
 
> set obs 200
 
> set seed 12345
 
> gen region = 1+int((4-1+1)*runiform())
 
> gen y = 10+(56-10)*runiform()
 
> xi: reg  y  i.region, noconst noomit
 
> **********************************************
 
> 
 
> I expect Stata to display the coefficients for all the four categories of the categorical variable named "region".  However, Stata still omits one category.  Is there something I am doing wrong?
 
> 
 
> I am running Stata 12.1 (SE) on Windows 7 platform.  I also tried this in Stata 11.2 (IC) on Windows 7 platform and I obtained the same result.
 
> 
 
> I will appreciate your assistance.
 
> 
 
> Regards
 
> 
 
> Jon
 
> 
 
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