R help - Jan 2009 - Categorical Variables and glm()

When including categorical variables in a regression, the default in R is 
to set the first level as the base.  Is there an option to specify a 
different level as the base? 

Regards, 
 
Stephen Collins, MPP | Analyst
Health & Benefits | Aon Consulting

	[[alternative HTML version deleted]]

Hi,

contrasts(yourvariablename)=contr.treatment(levels(yourvariablename),base=3)


3 is the number of the category that you want to be your baseline. Replace
accordingly.

Cheers,
Daniel


-------------------------
cuncta stricte discussurus
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Von: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] Im
Auftrag von Stephen Collins
Gesendet: Friday, January 23, 2009 12:10 PM
An: r-help at stat.math.ethz.ch
Betreff: [R] Categorical Variables and glm()

When including categorical variables in a regression, the default in R is to
set the first level as the base.  Is there an option to specify a different
level as the base? 

Regards, 
 
Stephen Collins, MPP | Analyst
Health & Benefits | Aon Consulting

	[[alternative HTML version deleted]]

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on 01/23/2009 11:10 AM Stephen Collins wrote:
> When including categorical variables in a regression, the default in R is 
> to set the first level as the base.  Is there an option to specify a 
> different level as the base? 
See ?relevel and the See Also's listed therein.

HTH,

Marc Schwartz