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Re: ROC curves in S?

To: Nicola Koper <nkoper@yahoo.com>
Subject: Re: ROC curves in S?
From: Frank E Harrell Jr <f.harrell@vanderbilt.edu>
Date: Thu, 08 Dec 2005 15:00:38 -0600
Cc: S-news <s-news@wubios.wustl.edu>
In-reply-to: <20051208205737.39535.qmail@web36209.mail.mud.yahoo.com>
References: <20051208205737.39535.qmail@web36209.mail.mud.yahoo.com>
User-agent: Debian Thunderbird 1.0.6 (X11/20050802)
Nicola Koper wrote:
Is there a way to generate ROC curves in Splus for
logistic regression calculated using GLM? I'm using
version 6.2.

Thanks,
Nicky

Don't draw the curve, which can lead people to select arbitrary cutpoints on the predicted probabilties and to use an improper loss (utility) function. But the area under the ROC curve is a good discrimination measure. You get it (C index) by

library(Hmisc,T)
library(Design,T)
f <- lrm(y ~ x1 + x2 + ....)
f   # prints C and other rank measures of predictive discrimination

Frank Harerll



************************************************************

Dr. Nicola Koper
Assistant Professor
Natural Resources Institute
University of Manitoba

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--
Frank E Harrell Jr   Professor and Chair           School of Medicine
                     Department of Biostatistics   Vanderbilt University

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