[R] odds ratio: how to create reference

Philip Twumasi-Ankrah
2008-09-23T11:50:32Z

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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--- 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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