Re: st: Categorical variable in regression

[John Ataguba <johnataguba@yahoo.co.uk>]

Thanks Petua for your response.  Maybe my question was not clear enough.  Note that I have suppressed the constant term in my regression - xi: reg  y  i.region, noconst noomit -.  In that case there is no problem of the dummy trap.  Based on Stata's documentation, the regression model I have specified is expected to run.  Unfortunately, it is not running for me.  

I look forward to more response.

Regards

Jon


>________________________________
> From: Petya Alexandrova <p.alexandrova@montesquieu-instituut.nl>
>To: statalist@hsphsun2.harvard.edu 
>Sent: Wednesday, 23 January 2013, 13:32
>Subject: Re: st: Categorical variable in regression
> 
>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 
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>>-------- Оригинално писмо --------
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>>От: John Ataguba johnataguba@yahoo.co.uk
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>>Относно: st: Categorical variable in regression
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>>До: Statalist statalist mailing <statalist@hsphsun2.harvard.edu>
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>>Изпратено на: Сряда, 2013, Януари 23 13:22:09 EET
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>> Dear Statalist members
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>> I have a problem trying to let Stata display coefficients for all the categories of a categorical variable in a regression.
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>> Consider the example below:
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>> **********************************************
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>> clear
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>> set obs 200
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>> set seed 12345
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>> gen region = 1+int((4-1+1)*runiform())
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>> gen y = 10+(56-10)*runiform()
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>> xi: reg  y  i.region, noconst noomit
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>> **********************************************
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>> 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?
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>> 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.
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>> I will appreciate your assistance.
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>> Regards
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>> Jon
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>> 
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