To select another reference level from the default that R chooses you can use the "relevel" function

example;

Reorder Levels of Factorwarpbreaks$tension <- relevel(warpbreaks$tension, ref="M")
summary(lm(breaks ~ wool + tension, data=warpbreaks))


function findlink(pkg, fn) {
var Y, link;
Y = location.href.lastIndexOf("\\") + 1;
link = location.href.substring(0, Y);
link = link + "../../" + pkg + "/chtml/" + pkg + ".chm::/" + fn;
location.href = link;
}

This sets "M" as the reference level for the analysis. At the prompt on the R workspace, type

?relevel 

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     But Rewards Everything

Happiness is not perfected until it is shared
                                                              -Jane Porter        


--- On Tue, 9/23/08, Bunny, lautloscrew.com <bunny@lautloscrew.com> wrote:
From: Bunny, lautloscrew.com <bunny@lautloscrew.com>
Subject: [R] odds ratio: how to create reference
To: r-help@r-project.org
Date: Tuesday, September 23, 2008, 4:06 AM

HI there,

i know this is a basic question, though i need some help because this  
is somewhat away from my current issue, but nevertheless interesting  
to me... Lets assume i have some estimated probabilities, say  
estimated by a logit model. i know i can also state them as an odds  
ratio.

Now i´d like to state these odds ratios as a reference to a specific  
outcome of my investigated variable.

for example, if my covariate of interest is race and possible outcomes  
are white, black and hispanic, whereas the latter are minorities in my  
case - how can i state the odds ratio in such a way that white is the  
reference (always 1) and other races' odds ratio are relative to the  
reference. e.g. hispanics are 1.5 times more likely to ...

Is creating 3 binary dummies for race the right way  ? And if so how  
can i go on.
As i said, i know this is rather basic, i am thankful for any links /  
references...

thanks in advance !

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